Have you installed the Inv. SP 1.1 + update?
Do you use Vault?
Yes, Service pack and update were installed this week, that's when slowdowns started.
We do use vault, that part of it is pretty good. I little lag when opening new files due to being stored on the network, but otherwise vault performance is good.
*edited for spelling
I would just like to confirm that I am seeing the exact same problem since installing Inventor 2013.
I am currently up to date with service packs and I also use the Vault.
The measurement tool lag sometimes takes over a minute to come back from unresponsiveness. I've also noticed my system RAM seems to take off and never come back down.