It looks like Nvidia is holding some Geforce GTX 260s back, as some partners have them but they are reluctant to send them to shops. They blame the last minute adjustments, but some separate sources have told us that Nvidia will give everyone the green light on the 26th.
After this day there shouldn't be any problems to find and buy the Geforce GTX 260, and this will coincidentally be the day after ATI releases its HD 4870 / HD 4850 series.
It looks that Nvidia will use any means necessary to try to spoil ATI's launch. The new GTX+ driver looks like a lot of trouble for ATI; and GTX 260, with its sub-€329 price will put a lot of pressure on the upcoming Radeon HD 4870.