The 2009 is where the big changes are. Nothing before that will have the handling or ride so get what you can afford. The 2009 is the best year so far, imho. Good upgrades to frame, wheels, and exhaust system and less EPA crap than later years.
You best ride for yourself. Many changes in 08. IMO. Especially if you can get a good buy used. Again, I would look for ABS, but that is sure to start a ruckus.
Wow to 2010 changes! Rented an Ultra in FL, but my bike is a keeper... So much in it! My sig does not show fairng, tourpak, and hard bags, whoops and lowers.
Plenty of deals in the'04-'06 range with low miles. Buy one and have a reputable shop bring the mill out to 95" w/cam and have 'em load a Baker DD-6 to boot. You'll come out ahead and still go head-to-head with the late-model bikes. Good Luck!
-Conan