Dell has been running specials on the Sony so that the price is around $200, which is only slightly more than the A520. There is a slight premium for memory sticks vs. SD cards, but the Sony includes a charger and 2 nimh batteries. It also seems fast enough that it wouldn't need a card reader for computer transfer, which the A520 definitely would. In short, price-wise it's a wash.
As far as features, the two seem really close. It sounds like the A520 makes better prints, but the S90 is pretty good, while the shot to shot time on the A520 can seem very slow, where the Sony is quicker. For secondary features, the S90 has a great movie mode, while the A520 has the very useful stitch-assist. One feature that seems unaddressed in reviews is the usefulness of the included software for OS X.
I guess I'm looking for a camera that's good at everything (ha!), but the primary purpose is getting baby pictures to relatives. Can anyone help tip toward one or the other, or suggest the ideal camera at this price range (<$250 with necessary accessories) that I've somehow overlooked?
(alternatively, someone can sell me an A610 for the price of the A520!)