At work we were puzzled because it took like 30 minutes to check out a clone from CodeBaseHQ. Granted, it was a 29MB repository with 4k files, but that's really not a big Mercurial repo. The official Mercurial repository itself checks out for people on IRC in like... 54 seconds over WiFi and it's 29MB with 2k files.
I discovered, though, that if I went to the deployment box, it took under 30 seconds. *sigh*
So if you're wondering why it takes so long, it may just be your OS. Figured I'd put this on here for google to crawl.
Yet another reason not to develop on Windows...