This weird problem came out of nowhere. I started VS2013, and it started to get really slow. Whenever I do something (write code, build, run etc.), VS gets really slow, hogging all CPU resources. If I let it be still, it'll get normal in about a minute. If I write some new code, however, the slowness returns.
I'm running Windows 8.1 Preview x64 with Visual Studio Ultimate 2013 Preview. I have no extensions installed besides the ones that come with VS. I tried resetting all settings and uninstalling and reinstalling VS, but it didn't help.