Actually, I might have got that wrong. It goes in .bitcoin on Linux, I think.
It always goes in your data directory, which is "%AppData%\Bitcoin\" on Windows, "~/.bitcoin/" on Linux, and "~/Library/Application Support/Bitcoin/" on Mac. As stated before, you can delete it once Bitcoin-qt indicates it's done syncing to free up a considerable amount of space. The
wiki page can give you more specifics if you need them, but it's rather straightforward.