I can play many of the tracks on the piano - I figured them out by ear, so they're probably not IDENTICAL to the piano collections arrangements, but they're still recognisable as their parent songs - but there are some tracks, like "Battle with Gilgamesh" and FFVI's "The Decisive Battle" that are just WAY too fast for me to figure out. I couldn't tell you offhand which songs I can play, mostly because my method of playing a song consists of sitting down and trying to figure the track out if I can't remember how to play it offhand, so I can probably play a lot more songs than I can list. I know for a fact, tho', that I figured out the famous "Prologue" which features in the ending of pretty much every FF except FFX, and that one took a lot of effort to work out.