After reading this blog post: http://blogs.msdn.com/shawnhar/archi...-gametime.aspx
I did a little experiment. One thing that stood out was when he says:
"We will call your Update method exactly 60 times per second
We will call your Draw method whenever we feel like it"
So, I just created a bool called drawCalled. I check for drawCalled in Update and only proceed if it is true (I reset to false). In Draw, I set drawCalled to true. It seemed to help quite a bit.
Note that I haven't experienced this issue on the 360, only on Vista.