Shawn provides a good summary of the features of bubbl.us and also speculates on the classroom value of bubbl.us:
I can see bubbl having a variety of pedagogical uses, both individually and collaboratively, both inside and outside the classroom. From teaching brainstorming in composition courses, to having students collaboratively trace the genealogy of the novel, to providing a graphic representation of intertexuality or patronage networks to accompany a lecture or in-class discussion, potential mapplications of bubbl abound.
Finally, Shawn mentions two other mindmapping tools: Mindmeister and Mindomo as objects worth playing with if we were so inclined.
I hadn't previously played with mindmapping tools but checked out bubbl.us immediately as it seemed to be something more exciting than revising the dissertation chapter I was working on. Using bubbl.us proved so easy and fun that I began using it to collaborate with Rachel Bowser on a conference panel proposal we had been kicking around. After spending some time with bubbl.us, I decided that I would check out Mindmeister and Mindomo as well. In the past week, I've made several different mindmaps in each of the tools, and I think I have a good grasp on the advantages and disadvantages of each of them.
These are all useful tools that could be put to interesting use in the classroom, for group work, or for individual (student or professor) organization. They are all free (although two have subscription options) and are web-based so there is no need to install new software and your work is available wherever you can connect to the Internet. Generally speaking, Mindomo and Mindmeister are very similar to one another. They both organize materials in a tree structure. They're very orderly and allow you to collapse different elements of your tree to reduce the complexity of what you've built. And some of these maps can get very complex, as you can see from this mindmap of dermatology on Mindmeister made by Daniel Nygren. After playing with each of them extensively, I'd have to say that Mindomo is the definitely the more powerful of the two, but it also has a steeper learning curve. Mindmeister lacks some of the features of Mindomo, but the trade off might be worth it because its ease of use perhaps makes it more appropriate for the classroom. You can see example maps I made in both Mindomo and Mindmeister for people whom Rachel and I needed to contact about our call for papers.
bubbl.us is not as polished as the other two platforms, but there's a reason that I've spent most of my time with it. It's the easiest and the most fun of the three. Rather than using a tree structure, which is fairly rigid in how you can position different elements in relation to one another, bubbl.us allows you to position its topics and subtopics anywhere on the map that you'd like. There are some features missing from it that are really important, like the ability to add hyperlinks or images to your bubbles. But on the other hand, it appears to not even be in Beta yet--although still open to public use. It will be interesting to see where its development goes from here. (Note to Google: buy this site now!)
I could go on and on about the different advantages and disadvantages of the three different platforms (and you may think that I already have). But I've decided to use bubbl.us to summarize all of this for you.
If that's a bit small for you to be able to browse the information effectively--and I suspect that it will be, although the zoom buttons in the upper left corner can help--then you can browse a full-sized version here. Unfortunately, you can't drag the bubbles around or start making new connections between things on my map. So I'll just recommend that you sign up for a bubbl.us account (or one of the others, if you prefer their looks) and start playing.