I've found several bugs in Lightroom's file import. All the ones I've seen appear to have been reported one or more times in Adobe's Lightroom forums.
The most irritating one I've had is where Lightroom fails to "find" a file and I have to help it locate it manually. This happens for about one image in eight when importing to a nested shoot.
A possibly related problem is Lightroom putting the copies it makes (when I say 'copy as DNG') into either of two places: the directory corresponding to the nested shoot, or else in a directory corresponding to the shoot name outside the nested shoot. Why it puts some files in one place and others in another I cannot explain -- I'm sure there is a pattern, but I don't see it.
For now I am happy that I continue to make backups of my files after I load them to disk, and before I let Lightroom at them. (This also lets me keep the original RAW files and DNG versions; Lightroom doesn't seem to have the option of including the original RAW file in the DNG when it converts to DNG; if that feature is hiding somewhere I've missed it.)
I also had this problem - Lightroom claiming not to find files that I had spent a couple of hours uploading......... and sometimes it finds the files but the image is shown out of focus...... anyone experienced this?
P.S. Contributing to the impression of unreadiness for release: it is documented that export/import of "photo binders" (name needs to change, yes) is not fully compatible between Lightroom on XP and Lightroom on OS/X. (Edit: I might be wrong here. It might be the library formats that are documented nto to be identical. But the export/import is certainly imperfect between the two platforms, losing rating information in at least some cases.)