I just switched from the Pre which I have used for ~5 months and have a few comments.
Before I get into the differences and the review - a little note about switching.
I called Sprint and told them I didn't like my Pre and wanted to switch to a hero, asking for the quickest and most painless way that this could be accomplished. I was told my only option was to pay the full non-subsidized price for the phone. I found this option unsuitable because I could cancel my contract and re-sign up buying the phone subsidized for a total cost of $260 ($180 etf + $80 best buy promotional price). I asked if I could just give them $260 and skip the canceling and resigning. The guy (from "executive" customer service) instead wanted to argue with me about how great the Pre was and how it was my own fault if I didn't like it. He did not want to move past that and help me buy a new phone.
At one point I mentioned the regulatory fee change that is happening in January and that it would allow me to get out of my contract without an ETF - but I was offering to straight up just give them $260 for the phone anyway. Our conversation went something like this:
CSR: A $.40 charge is not materially adverse. It would need to be a materially adverse charge for you to be able to get out of your contract.
Me: So what if I decide not to pay it?
CSR: Then we would send you to collections.
Me: So you can treat $.40 as materially adverse to you, but I can't treat it as materially adverse to me?
CSR ...
Keep in mind, this is someone who called me after emailing the VP of customer relations, not just a run of the mill CSR. Perhaps my request was unreasonable (although certainly not illogical), but I was surprised with how defensive and unwilling to help Sprint was. I decided that Sprint is much like a $2 hooker. They really suck, but they're so cheap you use them anyway.
I ended up buying the phone used for $200 off of craigslist. I'd love to hear how everyone else accomplished the upgrade. Someone else mentioned they got the phone for free off of an offer on another forum.
Anyway on to my thoughts about the phones:
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Things I really miss from the Pre:
Synergy: The hero has limited abilities to pull in Facebook photos/info for all my contacts, but it's not nearly as good as Web OS's synergy. I got used to always seeing someone's Facebook contact photo when they called, and it's not quite as good on the Hero.
Universal Search: Web OS made it very easy to make a call. Open the keyboard and start typing a name. You could quickly send an sms or place a call from the results. I still haven't figured out the quickest way to initiate a new text on the Hero. Holding down menu will bring up a keyboard on the home screen, and supposedly 2.1 will include a universal search function.
Keyboard: A hardware keyboard in portrait is as good as it gets, and I'll stand by that. I don't like the horizontal sliders, but I do miss the Pre's keyboard (even though it itself was not perfect). The screen keyboard on the Hero is an annoyance and I have yet to get used to it. It becomes very frustrating especially if the system is slow, bogged down, or otherwise unresponsive.
Card view: Oh sweet card view how I miss you. Multi-tasking on the Pre is second to none. Android has no clear way to tell what is running or allow you to quit things without installing third party software which, is itself, a bit klunky. The card metaphor had me spoiled.
Multitouch: Multitouch on the hero is non-existent in the stock rom and third party roms implement it in buggy and inconsistent ways. However, having to use buttons to zoom in google maps is still better than google maps not working at all, as was often the case on the Pre.
Camera flash: I take a lot of low light pictures, so this was a nice feature.
Things that are better on the hero:
Photos App: I can show people a picture I just took of them without waiting several minutes. Awesome.
Agenda widgets: A calendar is useless to me if the information stored in it is not made apparent to me. No matter how hard I try to constantly check a calendar, I will slip into not doing it after a while. As with Windows Mobile, Android allows you to download any number of agenda widgets that will show upcoming appointments right on the home screen - which I DO look at multiple times a day.
Guitar Tuner: Not a huge deal, but a guitar tuner app is something really awesome to have, and when people see you have one on your phone they are amazed. It's one of those "look what I can do!" apps. I downloaded gStrings and am very happy with it. I'm not sure it's even possible for something like this to exist on the Pre yet.
Augmented Reality: Also more of a "look what I can do" sort of thing. Augmented reality is a bit of a gimmick now, but in the coming months I think it will be used for more and more awesome things. You'll need to wait for Pre 2.0 (probably) to get this from Palm.
Speed: You do have to pay a little bit of attention to close things when the system bogs down, but normally it runs very quickly. For example, you can open the music application and scroll through all your music without waiting for 10 minutes while all the album art loads and then try to scroll through a choppy, unresponsive list as on the Pre. This is true of all applications, not just music.
Tethering: Web OS 1.2 broke the ability to tether over Wifi. The hero can do it without breaking a sweat, has a much nicer interface, and it more reliable overall with better features. This one is important to me.
Build: I didn't mind the Pre's build quality too much, but it did break on me (which was the straw that broke the camels back and made me want to get the hero). The Hero is very solid, but I am wary of the infamous loose battery door that some HTC's seem to have a problem with.
Micro SD: Expandable memory is not a bad thing.
Apps: I hate the idea of the carrier or the manufacturer dictating what apps I can install. Android's market is very agnostic when it comes to most apps, and you can install apps from any source after changing a system preference. Open development is critical to me, and I think it will be the thing that finally "kills" the iPhone (not that it will ever actually die anytime soon).
Custom Front Page: With widgets I can see the information I want where I want it. Awesome.
Overall impressions:
I love the Pre and Web OS, but the overall slowness, lack of significant updates, and unimpressive apps made it boring pretty quickly. I still think it's a great phone and would recommend it to someone who wants a "smart" phone but doesn't care about obsessing over it, downloading new apps, customizing it, etc. Basically, it's a great smartphone for most girls who want a smartphone.
Android feels a bit like returning to Windows Mobile, but vastly improved. It's still clunky in places, it still suffers from bizarre memory management and odd multi-tasking, but overall it's very stable and it can do a lot of stuff - much more than the Pre and much more than the iPhone.
For me, the switch was a definite win. I really love a lot about Web OS, but I think it needs another year or two of serious improvement and developer support to be a truly great platform. If Palm can survive that long then I would not be surprised to see them gain some healthy marketshare. Until then, Android is the way to go.
Hook it up!! 
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