I'm loving my hero. I went from an old HTC Mogul w/ windows mobile 6 on it. The battery started dying literally, about every 5 mins so it was time for something new. I've been following the rumors and dev. of the hero for the past few months, so I was pretty excited to get it. I did have a few concerns going into it though - 1. I was very used to a hardware keyboard, and didn't think I'd be able to get used to onscreen (i had messed w/ my buddies iphone a bit, and couldnt get used to his onscreen board). 2. Throughout development, apparently the sense UI was sluggish, so I was worried it would easily get bogged down when multitasking or not rebooting often.
I've been playing w/ the phone a lot the past couple days and both concerns were addressed. The keyboard is great! The predictive text input, as well as the option to use the full qwerty or dialer both with t9 made it a super easy transition for me. I'm pretty fully used to the onscreen keyboard after 2 days use.
As far as the sluggishness is concerned - I haven't run into any at all. The home screens flow very smoothly between each other, apps load decently fast, when multitasking, things still run well. I've been very happy with the speed and smoothness of the sense UI and the phone as a whole.
Overall, I am really really happy w/ the hero. I definitely prefer it over the iphone (and easily over my old Mogul). It is a very slick phone, hugely customizable, and easy to use. I think my buddy who has the iphone that I played with is a little jealous himself - and he's a huge iphone fanboy.