Welcome Fellow WebOSer!
I recently bought the Epic Touch and I'm pretty happy with it. I have had some time to get used to Android as I bought an Evo a while back. I still miss webOS, but the speed and utility of Android and the EPIC Touch make me miss it a little less.
As a guy new to Android from WebOS, you should look at this post from MiloMindbender. He was pretty active on the Precentral boards, and posted a really useful transition guide:
http://forum.androidcentral.com/general-help-how/33254-palm-webos-homebrewers-guide-android.html?
I found it helpful.
In answer to your original question, YES the stock email app in the Epic Touch does have a unified inbox. You can also grab another email client if you want to (K9 Mail has a similar unified inbox).
GPS is way better on this phone than the Pre. I think you'll be happily surprised.
On the whole I really like the phone, but I'll mention the few things that kinda irk me:
No delay to the Lock Screen: I can't put in a delay for the lock to come on if I manually turn off the phone. If I wait for it to time out, I can, but if I turn off the screen to put it in my pocket, then realize I want to check something or change a track, I can't with out putting in my Pin. Small, but really annoying.
No Camera during a call: I am not sure why Samsung decides not to include this, but you can't take a picture if you are on a call, or if the phone is on Low battery. Some people may not need this, but I was on the phone with my car insurance once and really needed to take a picture of the damage to my car and didn't want to have to hang up on my agent.
These are the only things that really bother me that the Palm Pre could do. There are a few other things relative to other Android Phones, but I don't think they are really important if you are new to Android.
Hope this helps.
Naa
Also, if you used the wave launcher in webOS, you should check out Wave Launcher. It makes switching open tasks a lot easier (in my view) than holding the home button.
https://market.android.com/details?id=com.mobilemerit.wavelauncher&hl=en