The full-face helmet I'm using is 1100 gms. and that's heavy enough. (of course, it's a cheap helmet that's not even imported anymore that I can find) I'll be waiting for the actual road-tests reports when Porthole and others start using this new Nolan. spyder
Daaaumm Spydy...is that helmet even DOT approved?

You didn't buy that when you were in 'Nam did ya?

The lightest FF helmet listed on the Webikeworld site is 1215 grams, and it's carbon fiber. If you can get by with a non flip face helmet, you can definitely save some weight. The mechanism (if it's worth a crap) to allow it to flip up is going to add at least 3-500 grams.
The very lightest Flip Face Helmet out there is here: http://www.webbikeworld.com/r2/motorcycle-helmet/lazer-monaco/ It's a great helmet, but only available in Europe...no US distributors that I have found. One of our UK or French brothers could probably arrange getting one for anyone wanting to try it out. The weight would be nice on that one. BUT, it doesn't have the internal sun visor, which is a really nice feature for me.
If you don't wear glasses, and don't need the Flip up (not modular...modular helmets are those where you actually remove the chin bar completely and store it away) for that reason, a regular FF is fine. I could never go back to a regular FF...I like them fine once on, but it's a PITA to take the glasses off, put the helmet on, feed the earpieces on the glasses into the helmet, etc. The Flips are the best thing since pajamas with feet in 'em...