Well, I have always been in favour of Twitter and am delighted to be back in fairly safe territory with Thing 7! I recently blogged about the merits of twitter here. It is an inspired solution to keeping current within the profession. It enables us to follow debates, trend topics, and take the power of information dissemination into our own hands. Of course, there are people who insist on micro-blogging about every micro-aspect of their life. As in real life, these people are best avoided (psst: just don't follow them!) Selectivity is the key. That, and deciding how you're going to use Twitter.
There are quite a few libraries on Twitter who use the tool to push information out to their users, both information specific to that library and often information about the interests of the readership in general. It is an immediate and current way to connect with our users. A change in opening hours at short notice, for example, is pushed out to users as quickly as possible. However, that relies on users 'following' the library. Because not everyone will want to do this, we cannot disperse with other methods of information dissemination. No one is saying that we shouldn't put notices up or update the library website homepage. Twitter is just another channel.
On a professional peer to peer level, I find Twitter invaluable. I would miss so many interesting facets of our profession and current debates without this tool. Twitter brings attention to projects and current events; one only has to look at the amount of Tweets containing the #cam23 tag to see how much interest we're generating!