I noticed this today on my user page:
20117 reputation 556 views flag weight 180
What is flag weight? I mean, I have an understanding of what it should be, but why would certain flags be more meaningful than others?
The base flag rating is 100. You get +10 rating for a flag the mods did something about, and -10 for an invalid flagging. Basically, mods will look at your flags first, and a lower flagger rating after. Anything around 100 won't be displayed. Source
At 0 weight moderators stop seeing your flags. At 500 weight you get a badge, then start gaining less and less weight for every valid flag you cast, asymptotically approaching 750.