if I had just one GTX 260, instead of the dual, then I would upgrade either to the 5870 or get another 260 about now...
But there seems to be a lul in the amount of games released that can actually use all that power at my resolution, so I will probably be keeping this setup for another year or so.
Also the way that the release cycles have worked in the past was:
1) Uber expenisve high end card comes out...
2) competition's answer to uber expensive high end card comes out
3) all high-end variants drop in price
4) process improvement leads to "mainstream" card that takes on the performance of uber expensive card (i.e. 8800GT vs 8800GTX, GTX 275 vs GTX280) OR new version of high end (4890) comes out, thus dropping the price of the old 4870 1GB.
5) Announcement of next gen drops prices slightly as retailers try to clear shelves.
I try to wait till step 4... which is prolly another 8-10Mos from now (at least), You get the best deals around that time.