I created a library twitter account (@camdencclibrary) a few months ago, and I'm happy to report it is now paying off: I'm starting to see our students, faculty, and staff on twitter.
For once, the library already has an established presence. We're not rushing to catch up, we're not trying to figure it out after a critical mass is using it, we're not looking at something from afar and wondering how it applies to us. We're there now, and ready for them. We're ready to provide a service in a serious, immediate way, and not as an afterthought.
I've noticed that higher education often acts when prompted by data, which is fine -- why jump into something blindly? -- but in this case I'm glad we didn't wait. We didn't poll students about whether they wanted the library on twitter, we didn't ask people what they thought of twitter and if they were using the service themselves: We built it, and they came (or at least are coming).
In the recent book What Would Google Do?, Jeff Jarvis outlines how companies must engage with their customers online or risk being completely defined by them. I think this applies to any entity selling a service. I understand that education is not considered a business in the strictest sense, but whether we like it or not our students, staff, and faculty are discussing our college online. I for one would prefer to be part of that discussion. Particularly when someone goes on a rant about something that went wrong for them (you know who you are), I'd prefer to be there to help as much as possible, rather than the person freely (gleefully, at times) trashing the college or library and assuming we won't respond.
This part of why I feel justified spending my time on twitter, despite the awareness that it might come and go, and that next year (or month) I'll be chasing down the next latest and greatest web tool. I truly believe it's important for the library just to be there.