The HD 3870 has clearly still got some breath in it. The price drops take it to a different level from the 8800GT along with the ability to get good performance out of them. When you even out the playing field with overclocked HD 3870 vs overclocked 9600GT, the picture becomes a little clearer with the HD 3870 really being able to come out ahead.
Ultimately though, the biggest advantage that the HD 3870 has is that anyone who is after a good motherboard is going down the route of Intel, in which case you'll most likely find yourself with a Crossfire compatible chipset. With the price of the HD 3870 moving nothing but south at the moment, the ability to get into Crossfire and see some extra performance can be done at a pretty good price now.
MSI have done a good job with the HD 3870; a nice little overclock helps give it a decent boost over the stock clocked ASUS card most of the time, whilst also helping the HD 3870 outperform the brand new 9600GT in some situations too.