I have to add myself to that list. The left-alt key just failed on my CM Quickfire with brown switches. Seems like a small batch of Brown, Blue and Reds have faulty left alt-keys.
From the CM rep in the Quickfire thread:
Edited by TomatoBasket - 12/3/12 at 2:30pm
Unfortunately, there was a very small concentrated batch Costar apparently had issues with left ALT. All issues have been fixed and it will not happen on any further board. We are able to track down the exact order these came in on, unfortunately it affects Blue, Red & Brown switches but in a very limited fashion. Also its impossible to recall the whole shipment because only about 1 out of 20 boards suffer the issue.
Please understand this was something we didnt catch, but do apologize, and assure you we have tightened up QC BIG time on our Costar boards.