Last week in Athens I attended a presentation by Julian Stuhler of Triton Consulting. I was of course aware of the support, but more from a DB2 internals point of view. It was great to get an external perspective on it from someone who has been working with it.
The key information is that spatial data can be points, lines, or polygons (including multi-part polygons). If you think about it, this is really powerful. One example that Julian used is that an address is a point, and a flood zone is a polygon. So now you can ask "is the house in a flood zone", which is "is this point inside the polygon"? Cool stuff! I can really imagine how this could be used by some situational applications to use data in DB2 alongside other data.
Complete documentation on the spatial features can be found in this book.