here's my concern with no SD card, which will not be for many already with one from past devices or additional purchase, is if you have to factory reset the phone (you know you have had to do it at least once) all memory is wiped. that includes pics, videos, music, apps, etc.
well, at least that's what happened with my tab 10.1 with no external SD card. i'll have to go over to the nexus s forum to see how they go about dealing with that.
with that said, make sure you get an external SD card large enough to match the internal storage, IMHO. and, lets hope that the software allow for move to SD, and default to SD for pics and such.