When rendering an avi...what is the difference between rendering under the "Good" setting and rendering under the "Best" setting. I know Best results in longer renders...but does it really look that much different than the Good setting?
Depends on what exactly you have done before. "Best" gives you bicubic resizing. So if you scaled a video or part of a video then "Best" is the better way to go.
I always leave this setting to "Best". Does no harm if no optimizing is involved.