Except that the 9800GTX+ isn't out yet, is slightly slower in most tests (close enough not to matter though), and the 4850 is already down to a pretty consistent $150-$160 after rebate. The cheapest 9800GTX on newegg right now goes for $175 after rebate, and most are still at $200. Keep in mind the GTX+ has a MSRP of $30 more than the GTX, and it isn't available yet either. Also, the 9800 needs a pair of PCI-E power plugs, while the 4850 needs only one.
Basically, it isn't an awesome card for the money, because it will be at least $50 more than the 4850 when it finally shows up, and certainly isn't available (much less easily available in any kind of volume) yet. As for PhysX? ATI is getting it too.