So far I have encountered 3 bugs, issues, quarks, problems since upgrading to LR 5. I didn't notice any of these issues with the beta. I think they may all be somehow related to the fact that I store all my files on an external hard drive array. This is all on an iMac quad 2.8 w/max ram running os x 10.8.4 with my library on my local ssd.
First, I wasn't getting the lightning bolt under the histogram for files that were PV 2010, but there was an icon there that said "file missing" where it should say "original photo" even though all my files were there and fully functioning. Also I tried making smart previews and it said smart previews were already made even though they were not and there was no icon for it. I seemed to have fixed this problem by running Disk Warrior on the HD. Those little icons are as the should be and making smart previews works properly.
Quark #2-If I delete a file from within lightroom (as I should) I get the proper popup window asking "Delete from Disk, Cancel, or Remove from Catalog". When I hit Delete from Disk I get another popup stating "Files are on a volume that does not support Trash. Would you like to permanently delete them." As if the files where stored on a network drive.
Quark #3-I exported a jpg file to Photoshop to work on and saved when finished. The file did not reimport back into LR5. At least not that I can find. I can see it on the HD right next to the original. I tried manually importing the file but LR will not allow it thinking it is already there. I tried all the different sorting methods and search in LR and making sure all stacks are expanded all filters are off. I need to get this file back into LR to finish.