I think it was not related to kernel anyway, but to tracker being buggy. During last 18 months with my N900 i encountered the same behaviour as you described at least two times. But before the reboots I changed in htop which process is messing my N900 - tracker was using almost 100% cpu (totally out of the blue) and when I tried to open media library it showed me either empty or "please wait indexing new media" dialog and told me to wait for infinity. After reboots then my library was also empty and had to do manual tracker hard reset. So it's rather some tracker bug, than kernel bug (just pointing it so others curious or afraid of installing can know that many of bugs in this thread are, in my oppinion, not kernel-related).