I said the SAME exact thing not too long ago. But then I started really looking at some of the things being posted on twitter by web designers/developers and found that a lot of it is quite useful. As a freelancer who is not plugged into the corporate world, I have found the information posted there to be extremely informative and interesting. Yes, there are crazy posts that I'd rather not see and it seems like some people are posting just to "hear themselves" (does that make sense?). But I have found some real gems for future web projects by reading others' posts.
I found out about this today via sitepoint's twitter that I would not have known about any other way: Sitepoint's Bushfire Relief Sale
Personally, between my 3 kids and my freelancing, I don't have time to read a bunch of blogs, so twitter is great for me. And a lot of times, bloggers will mention their blog posts on their twitter page and if I am interested, then I can hop over and read it.