I've found that this version that supports multiple cores is much faster than the original. Compare them yourselves, I have two WAV's compressing simultaneously at 16x each (-V 0 --vbr-new -h) on my MBP.
http://stimuli.ca/ituneslame/

The newest release of this app works beautifully with iTunes 7, thank goodness.

It doesn't work so well with iTunes 7.1 and later, unfortunately. There are alternatives, such as Max (which works quite well), but they don't work from within iTunes as iTunes-LAME does.

Incomparable MP3 converter!

You don't want mp3s, you want Apple Lossless

Mmmm.... Lame ain't an mp3 encoder. My favorite iTunes add on.

Not only does this work great, once I upgraded the built-in LAME encoder with a Universal Binary (available at http://www.rarewares.org/mp3.html) for my Intel Core Duo, it was really fast too.