One morning I fired up Visual Studio 2010, opened one of my solutions and found that the Visual Studio user interface was so slow as to be completely unusable. It took 5 seconds+ for each key stroke to appear, or to switch tabs or to do just about anything in fact. But only for this one solution. All of my other solutions seemed to be fine.
After spending a considerable amount of time in Google I finally found the solution to the problem. I deleted the .SUO file in the main solution directory and the speed returned to normal. No idea why.
Apparently, the .SUO files contain user dependent information, like the state of the solution explorer (collapse all nodes, close the solution, delete the file and you’ll notice that the nodes in the solution explorer are expanded again).