I've always wanted to do this - announce my stutter in front of a crowd. I've never had the balls yet, though, but I think it's really only a suuuper good thing to do for yourself! The crowd won't think any less - trust me. I'm sure you've heard a thousand times that "oh, we don't even notice your stutter anymore - it's just how you speak". So i'd say - DO IT! As to how, I'd do it with humor. If you're giving the presentation mic'ed up, say something like "if it sounds like the connection's bad, don't worry, it's just my stutter!". You can even do it if you're not mic'ed up "if I sound like a broken record/lag (whatever, choose your own thing!) it's not that - I just stutter"