I've had some serious issues with the framerate slowing down so bad that it was impossible to do much of anything, and when anything would attack me I had not chance of survival since the game would act like they weren't affected at all but wasn't acknowledging any of my commands. I have seen this in two spots so far, I don't recall the name of the first but the second spot was when I was tracking Mercer with the nitengales (pardon my spelling). It was awefull, I had to reload quite a few times before it finally stopped happening.
a handy glitch is a skeleton on an alter just above the Sightless Pit, when you investigate it (after killing it of course) you will find a book, it will never go away no matter how many times you take the book and if you search the skelleton, exit the menu and then search it again (reapeat as many times as you like) the books will just keep pilling up so you can take a ton of them at once. good way to make $$$
The other annoying glitch I've run into is that my bookcase downstairs in my house at Whiterun no longer works. I can't read or remove the books individually and I can't activate the bookcase itself anymore.