Seriously, when I first got word of this software, I was wondering what can I do with an application that helps me manage lists. I'm not much of a "manage my life using lists" person, but what I found really useful is the library of template of (some people will call it useless information) important / Interesting data, for instance the list of French Wines, or the Star Trek Voyager Episode guide and the very useful Shopping lists. I find these templates strangely useful, with the added support for images, the experience is pretty cool.
Here's what's new in version 5.0
They have versions for Windows Mobile Pocket PC, Smartphone, Palm OS and for the Desktop PC. Find out more here : http://www.iliumsoft.com/site/lp/listpro.htm
My only feature request is to allow lists to be created or updated by importing RSS / OPML feeds. That way someone can maintain a list of Magic the Gathering card prices (for example) and have subscribers to this RSS feed get automatic updates for the prices.
Some might argue that you should use a database and webservices for that but then again, ListPro is for non-developer types who just want some order in their lives :)