Well, I see all three versions pretty consistently. And truthfully I do see website more than any of the other two.
So, I looked it up in the AP Style Guide and here is the relevant entry.
Web
AP style requires the use of a capital letter when referring to the World Wide Web: Web site, the Web, Web page.
Who cares? Well, since the phrase We Build Web Sites is such a big part of our identity I thought I should get to the bottom of it when Kim asked me this morning.
There is also someone amongst us using the "website" spelling.
