Just popping in to say I've had mostly the same issues. Saving and loading are dramatically longer. I've had at least 3 or 4 instances of the "Saving..." progress bar popping up and the program either going straight to "Not Responding" or the progress bar just not filling up or even showing the "working..." animation to indicate anything is going on in the background. This has led to the project being corrupted twice in the last two days.
Lag is often and severe. Opening the animation dialogue, switching between animations, and creating a new animation are particularly bad, and when I close the dialogue, the Properties Bar spends 7-8 seconds cycling through the whole project and freezing once it gets to the end before I can do anything. Same thing happens when I delete an object from the project.
Steam overlay off, style set to basic, computer restarted, nothing helps. I would roll back to r250, but as far as I can tell, you can't do that with a Steam purchase.