Not me. I did give it some brief thought but I'm in no rush to. Infact I bought a CycloDs Evolution yesterday - the best of the best DS Flashcart - to replace my aging M3 Simply, and it isn't DSi compatible. So that's pretty much my decision made for me.
If I want apps etc I'll get an iphone or a Nokia 5800, which are both more powerful hardware. Seems to me that the Dsi was introduced to combat flashcarts as much as anything n'all, being that existing ones - ie. pre-DSi release - won't work for it.
I'm happy with my DSLite and CycloDS Evolution. Just need to get a decent sized/speed micro sdhc card - I'm looking for a class 6 16gb card that isn't sillypriced.