Damage Roms are not customized in the same manner as Fresh ROMS. I mean internally. Flipz really goes in and tweaks a lot of system files to make it more efficient where as Damage Roms (from what I can tell) usually just have apks thrown into them, at least in 2.05 and 2.06. Flipz will change about 10 things in the 2.1 roms (not detailed as he used to do in the 1.5 stuff), this usually leads to a faster feeling experience (transitions, more aggressive memory management, etc).