Many GTA V PC players have lost vehicles due to a garage bug that caused vehicles they drove from the street into their garages to replace their personal vehicles. Rockstar promised to look into the issue, and has reported it as fixed in the latest PC patch. It's unclear yet if Rockstar will replace players' lost vehicles or not.
The garage glitch is the most notable, but Patch 350.1 has fixed several other bugs as well, including an issue with the Steam overlay. This patch also improves stability, download speeds, and matchmaking. Although the patch notes do not mention it, it appears this update has also fixed the remaining problems with ambient occlusion.
Finally, the update has rendered GTA V PC incompatible with the "Script Hook" mod. Why, exactly, remains unclear. The simplest explanation is that the mod just needs to be altered slightly due to changes in the new version. Some players, however, worry it could be a deliberate attempt on Rockstar's part to stop modders--or perhaps an unintentional side effect of an attempt to stop the cheaters troubling GTA Online. Time will tell which is correct.
GTA V PC still has some bugs, but at least this patch has fixed one of the biggest. If you lost a vehicle due to the garage glitch, let us know if you contact Rockstar about replacing it.