Then you will soon be in the minority of internet users. In a few years, Facebook has the potential to basically BE the web for most people.
It doesn't stop you using other services/sites/etc -- you just don't need or want to.
Every time I hear this meme repeated, I get the (depressing) image of roughly 400,000,000 stub accounts that were created to check out FB, and promptly abandoned to gather dust.
That's okay. If a popular product doesn't add value for me personally, then I shouldn't use it.