The other day I had a sudden and mysterious slowdown in compile times within Visual Studio. When I didn't see an associated CPU spike during the compile, I increased the verbosity of the compiler and checked the output, only to see it pausing at a file copy.
Here I had added my project's SQL Express database to a library directory rather than the web site, so studio dutifully copied the database over. All this was fine, except that during development, I bulk loaded a ton of data, and the file was now about 240MB.
Note to self...don't copy 240MB database files as part of your compile. ;-)