I've had the extreme for about 2 weeks now, and I'm still learning its intricacies.
I've found I'm not particularly "saving" on herb, probably using more if anything. Granted, it is nicer than smoking, so you tend to do more, but I've always been the kind of smoker that only needed one bowl to get me solidly stoned. With the extreme I seem to need more to get me to that level.
I don't think I've got the whip totally sussed, because bags seem to get me more stoned more consistently.
I do like how the stone creeps up on you - you'll be doing your own thing, almost forgetting that you've even had a toke, and then suddenly realise you're very high - not like a bubbler which hits me pretty well immediately.
Also, does anyone elses Extreme make a very quiet, but audible, high pitched noise? The power adapter for mine makes this noise even if the unit itself is switched off and unplugged from the Extreme, and will continue to do so unless it is unplugged from the wall socket.