I just wanted to make a note here of something weird that happened to me and that could be a potential problem (I have no idea). I had created a new block and called it (unfortunately) course_section. I went to the admin/blocks page and deleted this block, then clicked on the Administration link in the breadcrumbs and my installation begain installing moodle again (of course there were errors since everthing was already installed). Then, when I went to my courses, everything was gone from the course sections--the stuff is still there somewhere, for example, you can go to the activities/resources from the links in the log tables, but it does not show up on the course homepage or the index pages. (Luckily this was a test site). After looking at my db, the only thing I could find was that the the last two fields in the course_sections table were gone (available and deadline).
Is it possible that because this block had a file called block_course_section.php, that when it was deleted it also deleted fields from the course_sections table? If so, then I'm wondering if this is a potential problem for other mods or blocks, or was this just a fluke?