Well, I just bit the bullet and ordered an Impression. Should be playing with it by the end of the week.
I'm coming from the original iPhone...so I'm a little nervous as to whether the Impression will live up to the iPhone as far as apps go. I'm not looking for the ability tp DL tons of useless apps, just a nice weather app & a movie showtime app mainly. Oh, and my guilty pleasure known as
lolcats 
I've been doing a little research on this site (which BTW is great!!) and am looking forward to the tweakability of the Impression. With the iPhone I'd jailbreak with every FW update, so I'll be doing lots of hack research on here. I'm sure I'll have lots of questions...but I'll try to make best use of the search function first.
Boy o boy, I can't wait to get my hands on the a877.