When I meet people that have something to say, and an interesting way of saying it, I encourage them to blog. But there's one big hurdle many people simply never get past: the actual writing.
I can respect that. Writing is hard. People spend their entire lives learning how to write effectively. It isn't something you can fake. It isn't something you can buy. You have to work at it.
That's exactly why people who are afraid they can't write should be blogging. It's exercise. No matter how out of shape you are, if you exercise a few times a week, you'll inevitably get fitter. Write a small blog entry a few times every week and you're bound to become a better writer. If you're not writing because you're intimidated by writing, well, you're likely to stay that way forever.
If you're still hesitant, I highly recommend John Scalzi's Writing Tips for Non-Writers Who Don't Want to Work at Writing, and Brian Marick's Hints for Revising. They're absolutely dead on with every point. Consider your writing a natural extension of your spoken conversations. If you aren't comfortable reading it out loud, rewrite it until you are. In the words of Elmore Leonard:
If it sounds like writing, I rewrite it.
Blogging isn't for everyone. But if you think it might be for you, don't let fear of writing keep you from doing it.