If it's grayed out it's because the application itself doesn't support moving it. The application developer has to enable it within the app itself. Some ROMS, like Bugless Beast (if I remember correctly), have it set up so you can force all the apps to the SD card, and putting an app on the SD card in no way affects its performance with very few exceptions (some widgets require being on the phone's storage), so why more devs aren't doing this is beyond me.
Heck, from what I've seen, storing the app on the SD card often uses less overall storage space than storing it on the phone!
Now, if I'm mistaken, someone please correct me, but that's what I've been hearing from everyone in the know and my experience backs it up.