Both in Whiterun, both have been widely reported.

1) Belethor's blank inventory: at some point in the game, when you try to trade with Belethor, both his inventory window and your character's inventory window will be completely empty. You will not be able to buy or sell anything to him. In my game, this bug occurred immediately after I brawled with him as part of a Companions quest (there is a mod on the Nexus that supposedly 'fixes' this bug. While the mod will fix Belethor to display his inventory again, his gold will never refresh no matter how many days pass).

2) Carlotta Valentia and her daughter stuck: at some point in the game, Carlotta Valentia and her daughter will become stuck somewhere in Whiterun. They will not execute their AI packages. 'Bumping' them will not fix the issue. In my game, this occurred after Carlotta followed me into Breezehome (many NPCs have 'followed' my character through cells, especially Breezehome since the front door is so close to the street, but she is the only one who got 'stuck' in the street immediately afterwards). Since Carlotta's daughter's AI package basically amounts to following her around all day, she's stuck too. Others have reported that it occurred to them after they completed her 'man trouble' quest.

Surely someone has uncovered the cause of these bugs? Anyone?