I do have all kinds of things in one record:
Files needed to make that prc (in ace or rar)
Txt with notes
Additional jpg; if I've found several pictures (maps, nice artwork...), I zip them up and make note in txt (too much bother to unzip just for the look inside).
Thought for a second about adding audiobooks also, but decided against it. Made instead new column for other formats.
Mobi is what I'm reading, so it's quality goes into column entry. After all, how can I know if a book has letters like é or some symbol without reading it? Lack of italics is easier to catch at a glance, still I don't see the reason for rating anything else than the format I (have) read.
Only recently I had a book with some greek letters, they showed up nicely in PC mobireader but palm could not recognize them. In (hopefully) far future when my palm is dead and I want to read it again, it's matter of seconds to unzip, change the html and create it again. Characters to search for I noted in txt file.
Also, pdf may look very nice, but convert into badly-formatted html->prc.
Maybe in the future I'll buy android phone and start reading epubs, it does not change the basic principle - I rate the format I read.