[quote name='xgsjx' post='981192' date='Oct 8 2010, 08:10 AM']There's nothing wrong with plugging your bass directly (with or without pedals) into the mic/line input on the iMac, I do it all the time.[/quote]
Me too, there's nothing wrong with it at all. I only ever use the mic input and its fine. I do use a Griffin Garageband cable which is a cheap, good quality cable designed for the job. Shell out for an interface if you want, but with a bit of patience, and by using some of the bass and eq presets that ship with Garageband you won't go wrong. Here's an example of my Traben going through the mic input only:
[url="http://www.ebaumsworld.com/audio/play/80714129/"]Traben Havoc - No EQ[/url]