Good comments here on a discussion that could go on forever. Agree a lot of it comes down to our expectations for the bike. Race equipment is designed to be lightweight, not to last forever, but most of us are sold race stuff when we walk into an LBS these days unless we specifically know we want something else. Anyone wanting a "lifetime" frame should probably avoid ultra-light anything, but as Alienator said, how many people really care to ride a bike for 100K miles over decades these days? Sadly, too many marketeers and LBS salesmen will tell us "don't worry, it will hold up fine, and if not, it's got a lifetime warranty".
Concerning the aviation/bike comparison, suppose everyone's experience is different. My background relates to production aircraft manufacturing, which is probably much different than those exotic one-off mirror frames for space telescopes. On the bike side, my custom frame bike was built by an aerospace guy, using a specific 7005 tubeset, welded by an aerospace certified welder using nitrogen back-purging of the frame along with the proper tig settngs and materials. It was artificially-aged (baked in an oven) to the time/temp specifications from Columbus, to restore the grain structure in the weld zones. The epoxy used to bond the pre-made CF rear section was the correct spec and well within date codes. The controls weren't all documented like a/c production requires, but I think the processing care was similar thoughout the build.
My guess is that C'dales CAAD processing specs and QA are also rigorous, including full-frame destructive testing on routine samples of production. I have a radonneur friend who's put something like 100K miles on a CAAD frame from the mid-90's. Of course, that's a sample of one, so doesn't really prove much other than at least one guy has ridden an aluminum frame a long time. Also dispells the myth that CAAD frames are "too harsh" for long distance rides, eg, 1200K non-stop brevets.
