I find the number of non-tracked quests in FNV most annoying. Sometimes you don't even realize you actually got a hint for one until you open the pipboy and look in your data section. After you look in your data section and notice something that could be a potential quest you can't remember where to go for the quest or who to talk to, or what to do sometimes. Then you can't remember how it started so you aren't sure where to backtrack too.

After reviewing my data notes in my pipboy this has happened to me a lot. All I can say is, its annoying. I feel like I'm missing in-game content now.

Also on another note, not sure if this is a bug or not. But when you finish most quests where they end and you get exp and they fade out in your quest log, well if you still go back to the npc's that were in whatever quest you just beat usually they still give you rewards. Now, correct me if I'm wrong here but shouldn't the quest end when you go back to the npc and talk to them? Why are they just ending, why do I have too guess if I got a reward or not? I don't think a lot of these quests were playtested. This has happened to me at least 10 times. Where the quest ends and I get exp, but if I go back to the npc that I did quest for I get a reward. Imho I don't remember this happening in fallout 3.