Users love feedback and the love real-time activity! At Metablocks, we always been big fans of user interface elements and widgets that convey real-time feedback! Digg Lab's Stack represents a great example (and a nifty visualization) of the potential power of providing real-time activity information. We recently built a similar visualization (naturally, inspired by the Stack) for a client in the music space to show real-time activity information on music tracks being played!

Simple Complexity's Chad Burt takes a slightly different view:

These are beautiful for visualizing the information they present, but there's one big caveat. This is all real-time information. Maybe it would be useful for Digg's own sysadmins to have this sort of information available, but for an end user it is just a pretty proof of concept.

I would like to differ, here is why:

• Users want to know what other users are doing right now!
  Real-time activity visualization does exactly that. By combining information about what users are doing and how many users are doing the same activity, this sort of visualization is a real-time gauge of what is popular.
• "Moving data point" in real-time conveys and reinforces the notion of real-time!
  Everyone wants a real-time system! Financial brokers want real-time information, law enforcement needs real-time data, and even the Internet consumer prefer real-time system. What many user interface designers forget is that user interface elements and widgets can be used to solve "marketing" or "communication" problems! Sometime "showing" your site or service functions in real-time is more important that the actual real-time information a user is looking at!
• Sometimes it's about the "Coolness Factor"
  Pushing the envelop when it comes to visualization definitely plays up your "coolness factor". Having user interface elements that do no interfere with the general function of your site or service, but play up the "coolness factor" and capture the imagination of your users generally cannot be a bad thing! With so many "me-to" sites and services, innovative data visualizations (real-time or not) can be a much needed breath of fresh air!