I don't blog very much because I am not that interesting, but ever since I started using Twitter I haven't had any inclination to write things here. Anything interesting that happens to me is instantly tweeted anyway so it would be redundant to write it here.
Blogs are useful for the occasional self-expression that requires more than 140 characters, but I find that I am pretty good at getting my thoughts and events across in a concise and informative manner by simply removing the fluff that is just there to make things read easier. Anything really interesting with lots of details is best left to a real life conversation anyway.
Also, "Blogs are verbose and not real-time. Just tweet the main idea and let imagination fill in the gaps." 99 characters. BAM.