I will go for Acer, though I do think you need to know what you are after. Acer themselves describe the Aspire 1671LMI (Yup, I bought that one) as a "Desktop replacement" This is marketing speak for lousy battery life. Around 40 mins in fact. Not a prob for me as I wanted a V8 under the bonnet, but with a P4 3Gig, the first job after booting, is to turn off the domestic heating system - you can see where that battery life goes. I remember seeing all those British Leyland strikers in the 70s standing around a brazier on a winters day. It is rather reminiscent of that.
The Acer 1671LMI is great - but if you need a real mobile capability, then aim for something with a "mobile" processor and avoid the P4 or Athlon 64 chips. The Pentium M class processors willl give a good two or even three hours away from base.
The other tip? Distrust any sales person. Written or brochure info is good, in that if it makes any claims, then you have a benchmark. With some spotty, white socked, commission driven sales droid, all you might get, is a shrug.
I would certainly have another - but I did my homework first.
Conan