Yeah, I've heard of some rediculous overclocks on the mobile 2500+.
I may (only slightly) disagree with the 2800+ not being a great choice for a regular Barton. Since the multipliers are locked now, the regular Bartons will have a realistic ceiling of around 200-210mhz FSB. (Of course mileage does vary with the quality of RAM and chipset used) At least with a 2800+, you're starting with a higher multiplier, so assuming the proper cooling is in place, you should, at least theoretically, have a little more MHZ to play with. Now is it as cost efficient as a 2500+? That's a whole other ball game. Just my opinion. :)
Main/HTPC: 880G Extreme3, 960T -> X6 3.5GHz, 4x4GB, HD6950, 2x120GB.OCZ.Agility3 RAID0, Sharp 55" LCD 1080p, Win7x64 Ult & Mint 13 Cinnamon
"Kill all my demons, and my angels might die too..." -T. Williams