Log of Time Machine activity? How to exclude one user account? (File Vault?)

I haven't done anything but browsing in Safari and a couple Spotlight file searches in the last hour, but my Time Capsule is suddenly backing up many GB of data and still rising. (It says, for instance, "7.2 out of 7.2" and both numbers keep climbing.)

Is there a way to tell what file(s) that might be?

My guess is that it's a File Vault account. I don't use File Vault currently, but I still have an old FV account on my machine from my paranoid days. And I did switch over there during this last hour to do a search. Someday I'll make room to switch that account from Tiger format to Leopard (sparsebundle) format--or else I'll take the time to figure out what old client files really NEED to be encrypted, move them elsewhere and get rid of that account entirely.

But in the meantime it's big old single-image File Vault with 10s of GB. All I want is to NOT back that user account up. I added the user folder to the Exclude list--and then logged in AS that user and added it to the list from there too, for good measure. And when I activate Time Machine, sure enough, I do NOT see that account in Users. And I never got the Time Machine warning that you get when you try to use TM with FV. So I thought I was all set to NOT back up that account.

And yet, after logging into that account and logging back out, TM is now writing 10s of GB of mystery data to my Time Capsule. I'm guessing this is not coincidence.

Question 1: Is there a log where I can test my suspicion that that's what is being backed up? Even though it's not showing up in the backup?

Quesion 2: Is there a way I can truly prevent that account from being backed up?

Thanks for any ideas!