The Celeron M does not have Speedstep so the battery performance is not as good as the Pentium M ("Centrino" if it comes with the integrated wireless). That said it's still a good choice as both are preferable over the Athlon laptops.
I've had two Athlon based laptops and even the "Mobile" version builds up way too much heat compared to the Pentium M. My fan runs most of the time, and I have to keep the laptop elevated to get enough cooling to keep it from getting too hot to touch.
Recently bought one of those entry level Compaqs for my dad. It was a Celeron M, but surprisingly quiet, ran very cool, and showed decent battery life. It came out to $400ish after rebate and all I had to do was yank out the 256 ram for two sticks of 512.
The Dell deals can be very decent too. I just got the 700M: 1.7ghz Centrino, 60gb, dvd burner, 2 yr warranty for ~$770 after everything. This one will be going from 256 to 1 gig of ram as well, it's much cheaper to upgrade yourself than to pay for it when you order.
