Some addons have issues with acceleration being installed, such as the Level D 767 (hence I only have SP2 installed instead of Accel at the moment)
But if you are a mostly default/ freeware kind of person there should be no issue for you. And even still I would imagine the majority of payware addons have no issue with Accel. But for me and my Level D, for the time being I'll just stick with SP2. I read recently in the Level D support forum that I think they have a fix for Accel now, I'm just too lazy to go about it

lol
I've personally not heard of any other issues with Acceleration, so you might as well install that and get the extra planes and missions. Well worth it.