Quad core stuttering?

I recently moved from a 3Ghz dual to a 3Ghz quad core processor. They're literally both rated for the same speed per core, the new one simply has more cores. Rendering\encoding\decoding operations are seeing marked improvement as I was hoping for, as are a few games.

Trouble is that some of the more basic operations like navigating windows, and browsing the web on google chrome are suddenly feeling inconsistent and... laggy is I guess the best word.

I'm seeing moments where the system seems to freeze up a bit for usually half a second at a time, it reminds me a bit of running my old celeron back when Windows XP was still new.

Can anyone offer helpful suggestions on what's causing this, or how to fix it? Nothing else has changed, my board was already AM3, since the Athlon X2 250 I was using was designed for it. Everything supports it already, so I'm still using the same 4gb of DDR3 ram... I just can't imagine why windows itself would suddenly seem a bit laggy.

Any suggestions?