VisualStudio 2010 close window performance

Finally I've got to the bottom of one of the Visual Studio 2010 performance problems.

Using Mark Russinovich's Sysinternals ProcessMonitor I cleared by environment down as best as possible and did some evaluation of what devenv.exe was accessing.

For some reason it's accessing the .proj files on a very frequent basis but it doesn't appear to be this causing the performance issue.

Using the File Summary option under tools though indicated that whilst closing a single editor tab there was just over 1 second being spent writing to the suo file - that seems very excessive.

Looking at the .suo file for the solution it was 1.2MB in size - hardly excessive but I guess it all depends on what it contains. I renamed the file and repeated the close of the editor window... almost no lag... a solution? Well possibly.

So what does the suo file contain? It's an OLE compound document and appears to contain a whole bunch of information persisted by the VS and any add-ins.

Have now been assigned a Microsoft Connect bug id of 619775 so will see if they accept and fix it.