I have had a (mechanical) problem with one SD card: it would work in one, but not in another Pi. In fact, I could install everything on the problem card and it would run for a couple of hours, but then, out of the blue started posting messages that looked like corruption of the file system.
I turned out that the problem card (Transcend SD HC 8GB class 10) was slightly bent on the side where the contacts are located. If I put it down on a flat surface with the contacts down, the center of the plastic was slightly higher then the sides. The other side of the plastic cover was flat. I assume the overall thickness of the plastic is less on the contacts side (and even not symmetrical) making this possible.
I am pretty sure that it was not caused by any abuse or ill-treatment, but somehow a result of the manufacturing/construction process.
After having slightly heated the plastic at the contact side end of the back (on the label side, not on the side of the contacts) and applying some force to straighten it (keeping pressure for a while), the card is now working without problems in both Pi's.