Blogs are more or less static once created – the initial text can only be changed by the original author, although people can respond in any way that they like. Wikis are potentially very fluid and can be changed by anyone who wants to at any time. It’s the difference between writing on the bathroom wall with marker, with people responding below with more marker, and writing on a whiteboard with people editing and adding as they like.
Blogs are more useful for news, for announcements, for event calendars, for book reviews, or for responses to a library pronouncement. Wikis are more useful for any kind of collaboration or shared projects. Blogs seem most likely to be useful for the entire library community – wikis are probably better for internal collaboration and use among staff. For instance, I would definitely use a blog to announce an upcoming event and ask for feedback. I would never use a wiki in that fashion due to the possibility of some person maliciously or inadverdantly chaning the announcement information.
