Hello folks,
I wanted to post this here - just in case it happens to someone else. I'm not sure if this is a bug in the quotes module, a unforeseen upgrade snag, or just bad luck. After upgrading to Drupal 5.1 and then upgrading the quotes module a few days later, I noticed that only the body of the quotes were showing up in my quote block. Strangely, quotes were not showing up as a type of content to add, and if you tried to edit an existing one, the page did not contain the node content - just the extraneous information - publishing options, notes, etc ..

After a bit of playing around, I found that somehow, the module and description fields for quotes in the table node_type where both blank. I was able to fix my problems by running this:

update node_type set module="quotes" where type="quotes";

Hope that helps anyone with the same problem, or a similar post upgrade issue with a particular node type.