I got a reply from Seibon and they say their GTI CF hood weighs around 100-110 lbs, so now if someone would just take their stock hood off and weigh it, we can end the "how much weight can I save?" question.
As for how easy it is to change a hood; it's not so difficult that you should be dissuaded from doing it yourself. However, it's not as simple as 'bolts out, hood off, hood on, bolts in.' You have to be careful when closing the hood for the first time. It's one thing to put the same old hood back on because you can line up the bolt heads in the original marks. With a new hood, there is a little play in the bolt holes to make the alignment work right. I recommend lining the edges of the hood opening with some sort of durable fabric to prevent paint chips when you close it. Also, don't slam the hood closed like my dumb a$$ did the first time I reinstalled a hood. You may get lucky and have it right off the bat, but don't be surprised if you have to reopen and realign a few times. Good luck though.