To be honest, from FM07 to FM08 there are hardly any 'improvements' worth noting in my opinion.
But that could just be me

....the best XI thing is signed sealed and delivered before it comes because I don't usually rotate all that often so best XI are the guys who play most games.
Adjusting the budget does come in handy sometimes when you are 1-2m short of that great purchase.
Probably my favourite extra feature is the pitch dimensions at the start of the year, I'm able to play narrow at the start of a new game and gradually widen my pitch as the quality of my squad gets better.
Facegen is a load of balls as far as I'm concerned, I really don't see what everyone loves about it. The freds all look like they were lifted from old PS2 games, they are blocky, not one bit realistic and it seems the same features get reused time and time again, all the facegens look identical!
FM07 is the better game I think, mainly because the superior match engine negates the extra features in FM08.