I did once, but I can't really tell you how it came out, because I overcarbed it BIGTIME. I never did get it tasting right. It seems to me like the beer would have been nice (it was a hoppy brown), if not for the gnarly carb flavor.
You've got it right, too....toss it in your first runnings, and leave it. From what I've read, it's roughly equivelent to a 20 minute addition. It does make your wort smell really nice while sparging! Unless I find some more compelling info on FWH, or just feel like using up some hops, I don't think it's something I'm going to mess with.