I think gilevans is looking at the hard links, which count as real files, so of course it seems like a huge backup every single time... but it's not.
Did you try my instructions above?
"Click on the [time machine] hard drive icon in the finder sidebar and get info. That will tell you the true size."
For instance... my entire TM drive is 29GB. But it appears that there are 33 backups of 5.6GB each (which would equal 165GB).
I have a MacBook Pro with that uses about 80 gigs of the 100 gig hard drive. When I first switched to Leopard, Time Machine backed up the whole thing and then did small multi megabit incremental backups every hour. I am using at 300 gig external drive. Then, suddenly, every incremental back up became 17 gigs. Within ten hours the entire external hard drive, which had been about half full for weeks, was filled.
What tipped me off that something odd was happening was that my internet performance was for crap all the time. Why? I back up over my wireless network to the drive attached to the Mac Pro in my office and these massive, nonstop incremental backups were soaking up my wireless bandwidth.
So...I erased all the backups off the external drive and started from scratch, and so far, the same thing is happening. It's like somehow Time Machine is not letting the file system know that it's backed all this stuff up. While it's backing up, when I go to Time Machine Preferences, the swirling "blue bar of progress" reads backing up x amount of 17.4 gigs. And it continues that way until it reads 17.4 of 17.4 backed up. Then it stops. When I look at the external hard drive, sure enough, there's another 17 plus gigs there.
I erased and backed up again a couple of days ago and then shut Time Machine off when 80 gigs of data filled 154 gigs on my external drive.