This is a question I've been thinking about recently. I used to blog frequently heck almost daily when I was at university mostly about the projects I was working on.
Twitter has been around for quite a few years now its only the last 2 years that I've used it, the last year more then ever. I love Twitter I'm always reading up on the latest developments in the web industry its great but your blog could lose out on your attention, its easy to tweet a 140 character message not so much to write a meaningful post. I've noticed that I barely write any posts recently instead using Twitter far more!
Twitter is not to blame I am! it's the convenience of Twitter that's very addictive, ultimately its up to me to write new posts in conjunction with Twitter I believe they can co-exist if used correctly. On the other side of the coin Twitter can be very beneficial for a blog spreading a great post quickly in short space of time.
A good post can keep visitors reading for weeks but a tweet lasts a few hours at best till it's buried with all the other thousands of tweets that are sent out daily.
Some things are more suited for Twitter then a post for example mentioning a good website and its link is great for Twitter short and to the point the same thing for a blog needs expanding for it to be really 'worth while' I think it comes down to the right tool for the right job.
What do you think?