+This sounds good in theory, but the fact is that neither I, nor some of the others who have been experiencing these large backups, have either of these conditions in play.+
There is a chance that if you post all of your apps and startup items that someone might recognize something that uses a lot of temporary disk space.
I found a Leopard compatible utility on Version Tracker called File Monitor
http://www.versiontracker.com/dyn/moreinfo/macosx/13657. I'm not familiar with it and haven't used it but it claims it will track file changes. It might be worth trying for those people who are having trouble with inexplicably large partial backups to see if it provides any clues as to what Time Machine might be finding as being backup worthy.
I hope that everyone who is having these types of problems are reporting them through
Apple OS X Feedback. It is an important issue and the more people that report it the more likely it is that it will get escalated for fixes.