I noted and reported a specific scenario where Intellisense just gives up the ghost. Don't know if it might be affecting you. It seems that if the namespace arrangement of your project does not necessarily mirror the folder arrangement of the files themselves, Intellisense gets a bit wonky at least in those files that are in the folders where the namespace does not match...
Of course it compiles fine and did not have that issue in VS2010...
I think intellisense in VS 2012 is just very flaky generally in ways that it never was in 2010.
My whole team has moved over to 2012 and on the whole are very happy with it (except the new TFS window - whoever decided that combining all the TFS stuff into one panel that you constantly have to switch context of and also change the 'pending check in files' view from using checkboxes to having to drag between 'included changes' and 'excluded changes' needs beating with a long 2 x 4!). The amount of extra work and mistakes my team have made using this is very annoying.
Adding more memory to our PC's definitely helped with some early perf issues and we've moved to SSD's now to really make it fly.
But, intellisense is one area that needs work. It constantly just stops working - 2 or 3 times a day for most of us. Sometimes closing the source code file and reloading it helps, but most times it's a full restart of Visual Studio. We have noticed various scenarios that can induce this, most of which involve having syntax errors in your code - my guess is that there's some unhandled errors going on in the Intellisense functionality for certain scenarios that just crashes or disables intellisense, but that's just a guess. It may be a coincidence, but things seem to have become better since update 1, but it does still happen daily.
I'm sure Microsoft will get it fixed, but it's annoying nonetheless.