I've been using AudioBoo (iTunes link) for a few weeks now, and I have to say, it definitely does what it says on the box: after a short signup session and the installation of the app to your iPhone, you can record and upload (and almost more interesting, listen back to others') audio quickly and easily.
You hit record, can talk for a while (i haven't hit a limit yet, though three minutes is what I originally heard, and that tends to be about right for these little mini-podcasts), then hit stop and upload, add a picture, title, and tags, and a few minutes later, your audio is right there on the web for everyone to hear. I've used it on my EDGE phone and my friend's 3G, and I have to say the experience is better on the 3G -- the upload speeds are much better (I generally have to wait on my iPhone until I get on Wi-Fi to upload the audio), and to my ears, the audio sounds better. Here's a recording I made at a Cubs game on my 1G with a few friends, and a recording my friend made on his 3G at a restaurant. Edge works, obviously, but the 3G seems to work better.
If there's a drawback to AudioBoo, it's that the site itself is pretty sparse -- while you can integrate your Twitter account and tweet about your "boos," that's about it. It would be nice to see some metrics about who's listening (how many listens at least) or something more social that just the following (and very rudimentary "liking") system that's there.
Still, they're just starting out, so you can probably expect to see more features in the future. My other quibble is that the app marks your location whenever you upload, not whenever you record, so my locations are all in the wrong places. But that's just a quibble -- AudioBoo is a simple and easy-to-use way to quickly upload audio directly from your iPhone. If you've heard anything good and want to share, check it out.
You may also want to take a look at WorldVoice Radio, which Steve profiled in detail earlier this week; it's coming at the challenge of 'micro-podcasting' from a different angle.