How necessary or important is it? I try to keep a running list of blogs or sites to follow, but a lot of the time I pull up someone's profile and notice there isn't anything there. Is it really important?

I understand are different levels of programming (from C/C++ system programmers to Rails and even Haskell and J) and not everyone works in a language easily worked with for web based applications. Not everything is web-centric, however with the advent of many popular and sometimes free services I don't think it's unreasonable to expect a majority of programmers to have a personal site.