Do I have to do anything different when flashing a ROM with Odin if I'm coming from CM7? When I first flashed CM7 on my SGS, I had an issue with my sim card and had to revert to stock.  However, Odin got stuck and I my phone refused to go into download mode (see my comment in this question for some details).  When I finally got it to go into download mode, I did the same as before but without re-partitioning, and it worked.

Does the fact that Odin got stuck on me last time I came from CM7 mean that I did anything wrong?  Should I have done anything differently due to the fact that I came from CM7?
I don't think so.  Usually repartitioning solves this kind of issue, so it's strange that the reverse was true.  I've seen recommendations that you should do a factory reset before and after flashing a new ROM, so you might want to try that.