I was just awarded the woot (enthusiast) badge on Stack Overflow, but I definitely didn't visit the site every day for 30 days. Here is my theory on how this happened.
When you open a new tab in Safari 4 it displays a new feature called 'Top Sites' which shows you previews for the front pages of your frequently visited sites. Stack Overflow shows up in my 'Top Sites', so I suspect that when Safari generates an up to date preview the 'visited today' count on Stack Overflow gets incremented.
If this is the problem then I doubt it's something that you can easily fix, but I thought I'd point it out.