Works Great with bulit in mic!
I was having problems with eTuner reading my built in mic, but after a few exchanged emails with their support team the problem was resolved very quickly.
If you have Snow Leopard and your mic is giving you problems, you may need to change the sample rate in Audio MIDI Setup > Built-in Input > Format to 44.1kHz instead of 16kHz. They informed me that this bug will be fixed in the next update.
eTuner is simple and effective, and a great alternative to a pocket tuner.
SP Gannon about eTuner