Deleted my old answer since, well, it got overridden, and invalidated by the flagger rating actually becoming useful to know (it gives you bonus mod flags, now!).
On your profile, beneath your gravatar and number of views, is your flagger rating. To understand the number, I'll quote Marc Gravell from the implementation post
[...]what is flag weight?
Simply: it is the way we order flagged posts. They still get looked at, but flags by known-good flaggers get seen first. We'll add this to your own profile shortly, but basically:
- start at 100
- +10 for a flagged post (+5 for a comment) that we did something about (or was basically valid)
- -10 for a flagged post (-5 for a comment) that we suppressed as invalid
- min 25, max 500
If your flag weight is low you can quickly recover it simply by flagging sensibly. "I disagree with this" is a bad reason to flag, as is "plz answer post is urgent mail me".
If you don't see a number there, then you are at an average flagger rating. That is, you're hovering around the default 100 area.