What is the sound difference between the Mic input, and the Line in input on the computer / for instance in recording. Is the MIC supposedly louder or get more "hum"?
The mic input is quieter. The line input is made for insturments that are run direct (no micing) such as a bass going through a direct box or a keyboard.
The mic inputs SUCK! Don't ever use it for serious recording! The pre-amps on a computer card, such as the SB Live! isn't good at all. You're better off getting a small mixer...
I was going to respond but it's been answered already. But yeah, the mic input has a preamp. If your mic, guitar, bass, etc is already amped don't use it. Also, they do always suck.