The satin finish on the top tube of my 2006 BMC Pro Machine SLC01 t started bubbling up, near the juncture with the red paint (see pic). I sent it back as a warranty repair, and BMC switched out to a new 2007 frame. The frame hadn't sustained any trauma, and it was bubbling on the inferior part of the tube, where nothing could have hit it. So it appeared to be a defect in the original finish application.

Also, someone else had a discoloration on their Trek:

http://www.bikeforums.net/showthread.php?t=283554