I've only had my new handset a couple of hours. Firing off a few observations.
Observation #1 - Setup is easy
If you have a Facebook and a Gmail account it's incredibly easy to populate your contact list, update phone numbers, and email addresses. If you don't, it'd be about the same degree of difficulty as any other smartphone.
I can easily link the contacts from my Gmail to my Facebook list and add phone numbers and email. For a particular contact I can link all this information together so that it displays together on the screen without having to switch apps or thumb between clients. WP7 organizes my data for me in an easily accessible way.
Observation #2 - Do it right the first time
If you have an xBox ID make sure you enter the information in correctly the first time. The only way to reset your Windows Live ID (that I could find) was to factory reset the phone and start over. Super cool being able to see my xBox stats, Avatar and so forth on my phone.
Observation #3 - Windows Phone 7 + Macintosh = Harmony
The WP7 Mac sync software works like a charm. I can drop pictures from my iPhoto or iTunes to my phone with relative ease. If you have a Mac and you're worried about not being able to sync your content to a WP7, you can rest easy from what I've seen so far.
So far it's just iPhoto and iTunes, no Contacts or Calendar events. (sad face)
Observation #4 - Gaming
As a gaming platform it has the potential to be superior in every way to Android or Apple because of xBox Live integration. Apple's Game Center looks tacky and useless next to WP7's xBox Live App. I've only played three games so far, but I'm sure I'll be downloading a lot more.
I can't wait to play Master & Student on it.
Observation #5 - UI
It isn't as cluttered as iOS or as junkie looking as Android. Every App I've used so far seems to conform to WP7's metro interface scheme. None of them have a single pixel of useless screen-hogging chrome.