I've been using a Nexus S since end January 2011. In no particular order here are some observations.

• Contrary to expectations the battery life is around 2-3 days for my usage pattern (infrequent WiFi, nearly no bluetooth and no GPS etc)
• The screen is a smudge magnet that is beyond description. The tiniest bit of smudge material creates a layer of unsightly swipes
• The screen area is good for the Kindle App. With the black background white text setting I can actually read books pretty nicely and that is a high usage pattern.
• The display is good and pretty rich if a color rich wallpaper is used.
• The only video I have is Eben Moglen's FOSDEM 2011 keynote and it plays pretty well (I had converted it anyway, read more here)
• Angry Birds, Paper Toss and Alchemy work well :) (as much I installed them for illicit entertainment)
• Touchdown works. Yay !
• The YouTube player is sometimes iffy on high resolution videos
• The TED app makes it easy to listen to a well curated talk list
• The actual physical phone hardware lends itself to a good grip once you can get over the lightness of it all
• The hot spot thing works nicely too. Didn't have more than two devices to try it out with though.The phone tends to heat up slightly.
• The stock browser is a bit of a bore and so I ended up installing and using Opera Mini (although I also installed Opera Mobile)
• The stock Android 2.3 UI is a bit of a vanilla one. In fact I quite liked the tweaks in the UI provided by LG (albeit on 2.2) with the pull down bar allowing one to quickly connect to a GPRS or, move into a Silent mode etc. In fact I am looking for suggestions on alternative launchers.
• The phone doesn't have too many external buttons (there's a power on/off and the volume switch) and that is a bit of a gotcha. When it comes to having to unlock each time to do stuff.
• I haven't had the call drop issue yet.
• Haven't used the phone to record a video and the rear camera works pretty decently (haven't used the flash on it). The front camera, as expected is heavily grainy