It hasn't. I had one instance of not being able to absorb a dragon's soul, and a flying mammoth right afterwards, but it's been fine since. There was also a spinning dragon during the weekend, but that's about it besides some framerate issues after I've played for about 5 straight hours. My save file is now 11MB.
Same here. I've had a couple of lockup/crashes, a couple of situations with lag (some, like having the entire Markath army chasing me - understandable), a couple of quest related issues and the bugs everyone else has been seeing (magic resistance, amazing backwards flying dragons). From time to time lag might get annoying, but not overly so and I can either wait it or just do a quick game restart.
That was a 12MB save file, 90+ hours of play. Lvl 41 when last I played it I think.
Just started a new one, about 12 hours in or so, getting close to the 6MB file. I'm intentionally avoiding the main quests and side quests, only doing the thief, dark brotherhood and daedric quests for now. So far like zero lag at all.