What happened was that your swap files were removed when you rebooted. The system starts with one swap file (size 80 MB) and creates additional ones (also sized 80 MB) when needed. Unfortunately, the system doesn't remove any of these when the memory load is lower. The only (?) way to get rid of them is to reboot (a more permanent solution would be to buy more RAM:-). You can find the swap files in the/var/vm directory.
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Stop the continental drift NOW!