I love a lot of those apps listed. sunrizer is awesome. It's the main one I know that allows you to have an entire fm synthesis editor that sounds professional. Comes complete with a software keyboard to play them back in whatever key you like, and works with the camera connection kit to control it with a USB midi keyboard as well. (Note: The song example here used no such USB connector. Everything you hear now used on-screen touch controls.) You can make your own invented sounds out of it, too. I actually plan to use that feature for an independent movie project I'm in the middle of working with.
Still, can't wait for the other apps to add the kind of sharing options that GarageBand has now. You can also output your entire mix, right in the iPad, to a file for which you can use as a single audio track in another GarageBand arrangement. Effectively giving you unlimited tracks in GarageBand and you don't have to copy anything out to another device to do it.
Another thing to note is that I used no other machine but this device to make the song, sign up for soundcloud, distribute the song, tell you guys about it, tweet about it, and put the link on my Facebook page. And still typing messages in this forum on it now. I could also put it in a movie now, with titles, and upload it to YouTube. So I think this latest update is a great one given that I can effectively do the gambit on an iPad alone, and easily.
So if someone asks you whether the iPad is worth it. I'll have to say, you'll hardly ever find another small device for the musician that is more cost effective. Not by a mile. I have equipment that to this very day, perform a single couple of functions the iPad can actually do, and I paid about the entire cost of the iPad to get it. Costs half the price of the iPad alone just to get one of the cheapest arrangements for a good quality guitar pedal rack. The Line 6 Pod on the floor performance rack. It can also function as a music sheet reader that you can use on a music stand (my first professional use of the thing). Dedicated electronic music readers can go for about $800 US.