Something similar happened to me today as well. I uploaded an album of mp3s to my iTunes and it went through the motions of analyzing and all that to incorporate into the library, only now the songs/album/artist do not display in iTunes. I tried looking for it as mislabeled or no label, and even sorted by date added to see if it was displaying. It. is. not. there.
However, it is there. Because I was able to download it to my iPhone via iMatch. Just not displaying in iTunes. Maddening.
Similar problem for me this morning. I pre-ordered an album on iTunes last week that was released today. When I opened iTunes the album began downloading and seemed to be successful as it showed up in the "Purchased" list. However, no sign of it my Music Library. I managed to drag and drop it in to a playlist, which synced with my iPhone no problem. I have played back the full album from the Playlist on the Mac and the iPhone, but no sign of it in the Library.
iTunes 10.6.1 (7) running on Mac OS X 10.7.03 with iTunes Match enabled.