Well I'd never buy a game for achievement points and other than slightly faster processing, they'd really be the main features of a 360 version of FM '08 over the PC version I'd imagine.
Alot of people complained on here about the last 360 version, particularly the lack of SI feedback and the 'save game bug'. It was eventually fixed but for many it seems that was too little, too late. I don't know what SI's position is on this though so I won't comment. It's a shame for console-only owners, but the current PC FM '08 is so darn good so far that I'll probably end up recommending it over anything to come between now and FM '09 anyway.
Personally I always prefered FM '06 for a better UI, match engine, display and simplicity, still play it to this day and count it as the best console footie management game since CM 02/03 on the old X Box.