Based on what I've read about the history of Laodicea, both hot and cold water served good, although different, purposes. The hot water was for cleansing and such, while the cold water was for refreshment. Lukewarm water wasn't good for much of anything.
In light of this, it would appear that Jesus was saying that He would rather a person be either hot or cold, seeing as they are both good things. However, He doesn't want anyone to be lukewarm, or a "fence-sitter".
It should be noted that both hot and cold water are mentioned in the Gospels. Christ talked about a person giving one of His followers a cup of cold water and not losing his reward for it. Also, hot springs are associated with healing. Again, both hot and cold water are good, but lukewarm water is not.
$0.02