in my experienceReally though, GarageBand is a grokkable composition and arrangement application offering you some flexibility in modifying, tweaking and embellishing the (MANY) loops provided for you. And you can add in your own noodling with a keyboard and microphone, but I'm inept and will mercifully keep my talent out of the ears of others. And again, in spite of that, I was able to fool my wife into believing that I created the music and she was actually interested in knowing how I did it. I don't think i want to show her because the bloom will be off the rose at that point, and I think that might be the Achilles heel of this application for the masses out there (ie, I don't see any Billboard hits coming out of this app, but who knows...)
What I'll really be looking at when I use the app and when I hear the songs created by GarageBand users is the compositional quality and arrangement skills of the song and author. Lots of electronic music out there is anchored in composition with a veneer of beeps, twitters and synth chords (a delicious collection to be sure) so, I figure that I'll be able to use GarageBand for a long while without missing out on the creative process that is solely based on loops arrangement (in my musically untalented case, maybe not yours). There's enough value in that for me to justify the price of iLife 04 (of which GarageBand is a part).
In terms of user interface, I utterly loathe the wooden UI elements surrounding the main application. It's cheesy, ugly and matches nothing else in the Mac OSX software pantheon, and the brushed metal theme on other iLife apps don't fill me with dreams of derivative experimentation (like Kaleidoscope did for some reason). Luckily though, the app is simple enough to allow for this multiple document interface paradigm (I loathe that word more than any other). Adding in tracks and fiddling with output levels and timing is pretty straightforward, but the process of importing loops or other sounds is completely undocumented (afaict).
After using offline help (and failing) and online help I was able to figure out how to import loops into GarageBand thru drag and drop. Just drag a folder of loops onto the loops area of the window and it will import them. However, it won't highlight that area when you are dragging the folder over it, so you have no indication that you are doing the right thing. There is widespread absence of contextual hinting in the app's UI...
Still though, it's a fun application to use and it passes the 'wake up' test for me, which works like the following...