We like PS3 dynamic themes. (We don't like paying so much for them, though.) However, ever since the initial batch of themes for LittleBigPlanet, WipEout HD and PixelJunk Monsters, we haven't seen many interesting themes for purchase. That's about to change with the upcoming Modern Warfare 2. Infinity Ward used Twitter to confirm that, like all games released in 2009, MW2 will feature both rumble and Trophy support. Additionally, they noted "some dynamic themes [are] in the works for the PS3 XMB."
Considering the popularity of the Call of Duty franchise, it seems likely that the Modern Warfare 2 dynamic theme will be quite a popular item on the PlayStation Store. We can already see the hordes of people downloading the theme whilst they type up yet more annoying (and incorrect) PSN spam chain letters about how Call of Duty is becoming an Xbox-only franchise.