It has a longer battery life, but I've had a couple friends with acers and I haven't been impressed. Both friends had troubles with them within a year, and both had further issues with customer service.
It will vary from person to person. HP's been extremely dodgy with me about honoring warranties. They went as far as to say that they wouldn't honor it. At the time, my computer was only 6 mos. old and the part was covered (I also bought their extended coverage to cover more things and for a longer period of time). That being said, before and after, I've never had a problem with HP.
I have the acer and am pretty satisfied with it. I haven't had to call IT or anything for it though so not sure what would happen there but as far as the compact laptop deal, I think it's pretty cool.
out of all mentioned so far i'd go with hp.
the Eee pc's by asus are far better built than anything mentioned so far imo though. same exact configuration but somehow works better, faster and seemingly more reliable at this point. the one i got for my son boasts an 8.5 hour battery life too.
My wife and I both have the 8.9" acer...which is the same chassis as the 10.1". We bought the first one a year ago, the second 6 mos ago and have had no problems with them. We love 'em. I also have a coworker who bought one at the same time and is buying another for his kid.
Tiger Direct frequently has deals on refurb'd acers. The latest was the acer 10.1" with 1GB Ram and 160G Hard drive for $289 w/ free shipping.
FWIW both of ours are refurbs...
I don't buy extended warranties, but Tiger does offer them on most items.