I have primarily been using mine for Musick (if you want to call it that).
I'm working on upgrading my A600, and am awaiting parts of my 1200 upgrades.
I have been using OctaMED Sound Studio with a MIDI interface.
Before too long I will be controlling my Atari 2600 via the MIDI, at least that is the plan. We'll see how it all works out in the end when my 2600 MIDI adapter arrives.
Aside of that I use it for games, writing, and IRC.
I do have some animation software here that I'll eventually tear into as well.
It's amazing what you can do, even with a stock Amiga 1200!