A lot of fans of a cappella groups are fans just because they like the music. Others have crushes on group members, or, if you're really fortunate, follow your group just because it's the cool thing to do on campus. While these conventional means serve many groups well, there are other, proactive ways of solidifying an audience, many of which are served well when a group chooses to blog.
Blogging allows a group to share its story. Liken your a cappella group to your favorite television show. Do we like shows with good writing? Good acting? Good special effects? Yes, yes, and yes. But does any show become your favorite based on these factors alone? More likely, you're drawn into the story of what you're watching. You want to know whether Ross and Rachel will finally end up together. You want to know if Fox Mulder ever will find his sister. You want to know if Jack, Kate, and Sawyer ever will find their way off that darn island. The storytelling aspect of blogging about your a cappella group is similar. You discuss the process of learning music, of coming together as a group, of your journey through the ICCAs. Such stories make you more than just a group that knows how to sing, but a collection of people on a journey that your fans can follow along with.
On the note of presenting your group as a collection of individuals, consider capitalizing on the appeal of personal narratives. No, your group blog should not deteriorate into a LiveJournal whine-fest of group members pouring out far more information than anyone will care to read. It should, however, give fans insight into who the group members are so that they'll be all the more eager to celebrate the group's accomplishments and come to shows out of an interest in seeing the connections between real people they've read from and the performers on stage.
Blogs are generally only useful when kept relevant, so don't forget to update your blog on a regular basis. If you use it consistently, tell your stories, and let your individual personalities shine through, you will likely be pleased with the results.