In reply to Pids:
I've had 2 replacement frames from Gary Fisher, so can assure you that they do honour the lifetime guarantee. Yes the brand is now less distinct within Trek (a mistake IMHO), but that hasn't changed things. In fact Gary Fisher now claims he gets to run the whole company now !
In both cases the breaks have come on the chain stay
With the first one (a Tassajara) I contacted them via their website, explained that the shop where I bought it had disappeared, but since I was able to find proof of purchase they arranged to send me a frame to my nearest dealer.
With the second (a full-suss) I thought I would simply need a new swingarm, but the shape had changed and I ended up with a new frame and various new components.
So first step is the shop where you bought it, but if they aren't around you'll need to go to your local trek dealer with some proof of purchase.