This hint doesn't accomplish anything, but if you tap the graphical representation of the mic on the screen in the Voice Memos App on the iPhone (OS 3.0), the VU meter registers just like it would if you were tapping on a real mic. It doesn't register anywhere else on the screen, though; just on the mic.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20090623135704772