I'd go with the 40 because it's slimmer, lighter, hence even more portable, and the shutter lag is much less - this from my handling of the two cameras. Else there isn't too much difference in terms of still picture features.
If you're not planning to print larger than A4 or cropping a lot, I don't see much point to the additional megapixel. I also feel that both the 30 and 40 take nicer looking pics than the 400 and 500 before them.
It's a good point about the memory card bit but SD cards are so incredibly cheap these days!