I've been at home today, using up one of those spare days holiday from your quota that you have to fill before the end of the year. About an hour ago, I realised that I haven't actually spoken to anyone all day long.
There are lots of pros and cons for answering each and every comment / tweet or email. To answer each one (or the vast majority there of) means you are visibly present for your followers and have a genuine interest in what they have to say to you.
If you don't answer them, you can run the risk of making your followers feel that there opinion doesn't count. However, it does mean you can free up time to write new and topical content.
Seth Godin for instance does not include comments on his blog: Why I don't have comments
What do I think? I think the age old 80/20 rule holds firm here, with 20% of bloggers writing 80% of the content. I'm going to keep on commenting on blogs that I want wherever possible. It's interesting that as soon as you start asking the question, more and more people start getting onvolved anyway. Especially on Twitter!