Since I have had Fallout NV I have noticed the same glitches that are still present in Fallout 3 even with the patches. I remember once in a blue moon I would see a flying rad scorpion in fallout 3. After about 2 hours in Fallout NV a giant rad scorpion appears out of thin air (literally) when I'm in Goodsprings. Then there are moments where the game freezes for no reason, characters in town wander off and die, merchants like Chet and Johnson Nash can magically restock there supply of items in seconds and enemies that you kill in a building like the Bison Steve as soon as you leave the building and then a minute or two later you decide to go back in the enemies bodies and their equipment are gone. And my personal favorite floating trees and other objects.
These are just some of the glitches and I think most are due to the game being really good. The game is extremely well detailed so that every side of building every rock and NPC and item is uniquely different; plus there is a lot of small detail objects like cups bottles plates etc.. One of the results of this over detailed world is that your character in the game often lags around the game kind of like a laggy multiplayer match in Gears of War where you character sometimes goes horrendously slow and then all of a sudden he'll be warped ahead really fast. Another thing I've noticed is parts of walls sidewalks and shadows will flash or blink. This flashy effect is produced when textures overlap. For example you have a piece of brick wall and then you have a piece of painted drywall and they are put in the exact same place so the game isn't sure if the brick is supposed to be showing or the drywall.
I have worked with the FCIP and Farcry 2 map editors so I kind of know how bugs and glitches can occur in a videogames which is why I can sympathize with the developers, they made a giant open world with so much and the more you put in the harder it is to keep track of all the stuff in the game. I remember after I would make a map I would beta test it with my friends in an XBL mutliplayer match to see what needed to be fixed, and a lot of the times it was small stuff like flashies or floating objects and I was working with a small area and it would take me hours to fix those things. So I can only imagine how long and how hard it would be to fix a lot of the stuff in Fallout NV. However, as I said before I am noticing that a lot of these glitches are the same as the ones in fallout 3 which means that both games were created using the same engine which means that possibly the only way to get rid of these glitches is to make a brand new game using a newer and better engine one that can handle all the wonderful stuff that makes up a fallout game. Unfortunately that would be a really big headache having to mass produce a game that has already sold a million copies.