Actually, "three times consecutively" is somewhat inaccurate.
3DES is DES run forward, backward, and forward again. While
running DES forward and backward with a single key gets you right
back where you started, if a different key is used in the unencrypt
(backwards run), it scrambles the data further. (see randombit's
excelent explanation below.)
While DES is horribly out of date and should not be used for
anything beyond kid sister encryption, 3DES can hold its own
against more modern algorithms such as Blowfish and RC5.