I did not have any issues with idml files. It is uncomfortable that your files are untitled and missing links do not have low-res visuals in the frames but so far, so good.
CS6 on the other hand really does my head in. Indesign gets really slow sometimes for no good reason, Illustrator has the usual 'upgraded' features that make me wanna jump off a bridge (having said that, cs6 IS actually a step forward from cs5 because they brought back some features from cs3) and Photoshop refuses to save files 'because of a program error' which I then easily can save in CS5...
No CC here, and I doubt we will have it in the foreseeable future, so I couldn't really tell if idmls from CC open up with issues in CS5.5