I have blogged about dynamic segments in WebSphere Commerce a few times because I think they are extremely powerful and allow marketing to do all kinds of very cool things to make their site more interesting to a buyer. The InfoCenter has a really good page with three great examples for how the rules for dynamic segments can be constructed. Remember, this is in the Management Center and these flows are constructed with basic drag and drop gestures.
In the first example you want to categorize your customers according to the type of sports equipment they buy.
In the next example we use searches for a particular manufacturer to build an interest group that is targeted for manufacturer promotions throughout the store.
The last example you can use the Add To Or Remove From Segment action to create dynamic, time-sensitive customer segments based on individual customer behavior. Here we target new customers who just register and then put them into a segment that is targeted for 20% off during the promotion and once the customer purchases something during that promotion they are removed from the segment.