Well, mine might sound logical, but I am NOT from Santa Cruz.
I am an avid Mountain Biker, and own my dream bike - A Santa Cruz Bullit.
I was trying to get a login for one of those popular sites about 5 years ago that you can never get what you want, unless you want to add 49889 to the end of it, kind of thing. And I hate putting nubers at the end of my login/screen names/etc. Then, I tried Santacruzer, and have used it ever since.
I have only ever ran into a problem once with it, and did end up being Santacruzer2.