Probably going to go from v3.0.2 or 3.2.2 to 3.5.1. If your center display doesn't show the outside temp next to the clock, then you're on 3.0.2 and can expect to get the temperature display there. Outwardly that's the first thing that you'll notice. Other than that, voice commands are reportedly (though not for everyone) MUCH better. I can attest to this; my voice commands haven't ever been bad but they're much better with the latest update. They're also simplified, not needing you to specify input or type, i.e. if you want to play an artist on your iPod, just say Play (artist) or Play (song), keep in mind that if the artist has a self titled album, it's going to beep at you and it wants you to specify though it doesn't pop up on screen with any prompt.
Just play with it once it's updated and learn some of the new stuff, it's pretty neat. Every update gets closer to where it should be.
2012 SGM SEL Sedan 303a w/o Nav | Job 1 built 6/2011
FSWERKS Cool-Flo w/ ITG Filter | FSWERKS Stealth Exhaust | 17x7.5 Axis Sport XMX Graphite wheels
Sonic Crew #28 | Rally Revolution #117