If you do a Google image search on "GT Avalanche frame cracking" and look at the first and fourth images, for reference....
The first frame (a 2005 Avalanche 2.0 Disc) cracked around the head tube. At first I thought it was an elaborate scratch. I didn't think cracks could appear across a weld. After some Googling - I found pics of the near-exact same cracks in other's frames. Quite a common place to crack apparently
The latest frame (a 2007 Avalanche 2.0) is developing a crack around the weld between the BB shell and the seat tube. Again, a common place for them to go.
If these were steel frames, I wouldn't worry so much - just get them welded back up. But when Alloy frames go, they give very little warning and it's not worth welding these when I only pay between £20 and £40 for a second hand frame anyway.
This will probably be the last time I buy a second hand frame in alloy. At the moment, I am looking at buying a new steel frame - probably an On One Inbred