After using iChatStatus long ago for setting my status to my current application (and after it broke in Tiger and since Tiger had the functionality of setting your status to your current song and the author of iChatStatus decided to not make it work with Tiger because of that and this is a really long sentence...) I finally got around to making a little AppleScript that sits there watching the finder and updating iChat with your current app every 10 seconds.
You can get it here if you want to try it out. Stick it in your Login Items in your Account Prefs, and it'll start when you log in. My only problem is that I can't get it to hide from the dock. The checkbox to hide the little script in the Login Items doesn't hide it. I also tried to put some code in there to try to get it to hide, but it doesn't. If anyone has any clue, feel free to tell me :)
Oh, by the way, if you haven't got an Apple, you're missing the boat, man.
I got instructions on how to remove it from the dock here.
Also, my incarnation of a similar script. :)