Yes, we've used it. But it's very difficult to use quickly in real time and the audio is not good at all.
Ok, well I've got to chime in here.
As for "difficult to use quickly in real time" I can see where this comes from - maybe - but seems like an inflated claim. In OneNote, there's a button to display the recording toolbar, which has the usual play-pause-stop-record buttons. Two clicks to start recording (one, if you had the foresight to turn on the audio recording toolbar before you started notetaking) doesn't seem to me to be "difficult to use." There's no keyboard shortcut, though, which is a bit annoying. Switching between notes while recording can also confuse things. But for the most likely scenario - recording on a single page while you take notes - OneNote's audio recording is perfectly usable.
OneNote's audio quality is skewed out of the box to produce small file sizes, so the quality is limited, though OK for spoken audio around a conference table or with a clip-on mic. However you can tweak the audio quality to be as high as you want. Bumping up the recording parameters gives much better quality audio, albeit with a slightly larger file size. You also get to choose the codec that will be used to encode the audio. It defaults to the Windows Media Voice codec, again assuming spoken word recording. But you can use the regular WMA codec for better quality.
Microphone quality is a much bigger factor in quality of audio anyway. No program is going to work magic with the crappy audio you'll probably get from a laptop's built-in mic. For recording something like a lecture, an inexpensive external mic would be a better investment.
When you play back the audio, the app will highlight the text you typed as the recording was made, which is neat to watch, and possibly even helpful. There's even an add-in that lets you tweak this timing if it somehow gets unsynced, or if you're extremely picky and have lots of free time.
My biggest gripe with OneNote's audio is that there's no audio meter in the program, so it's not easy to see what level you are recording at. If your mic is set to low or too high, or your external mic is not completely plugged in, causing you to record either buzzing or the sound of your own typing via the built-in mic, you can't really tell this while you are recording. (And yes, I 've had all of these happen.
For things like lectures or meetings where you've only got one chance to capture the audio, this is a major oversight. Since OneNote just uses the system audio settings, you could theoretically run a separate app or widget to display audio levels during recording. I've been looking for such a thing for a long time though, and it doesn't seem to exist. The recording level gauge built into Windows is too klunky and hard to access to be of much use.