My roomie has one. I haven't been able to justify moving up from my Advance SP yet.
I played mario kart online once, on the shitter (so awesome!) and got my ass handed to me. I've yet to try online again. Mario Kart for the DS could be my favorite Mario Kart EVER. It's tracks are all very rich and original, plus it has unlockable tracks from every previous mario kart game ever.
I have played the new Super Mario Brothers extensively and LOVED it. Very cool and innovative useage of the touchscreen on the mini games. As well as the microphone. (blow into the DS to inflate baloons etc)
Overall I lean towards the "lite" for esthetics of course. But I hear the original DS is much more comfortable.
For schizzle. I have one and Will has a few too. We should play at his place (He's got a nice tv) We could combine it with "Dress up as construction workers and make lewd comments at girls walking by" day.