Although it was scheduled to appear on retail shelves today, it appears that the market availability of Nvidia's GTX Titan Z has been delayed due to last minute design changes to the cooler, according to a report from SweClockers.com.
Judging from the pictures of the GTX Titan from GTC 2014 and retail pictures, it appears that Nvidia jumped the gun thinking that it can cool two massive fully-enabled GK110 GPUs with a 2.5-slot cooler. The new picture of the cooler taken from retail press shots shows a new, thicker triple-slot cooler.
AMD definitely had a same problem with its own US $1,500 price R9 295X2 dual-GPU flagship with two Hawaii XT GPUs and went to Asetek in order to create Project Hydra, a hybrid closed loop water cooler with a fan that takes care of the memory, VRM and the bridge chip. Nvidia on the other hand did manage to retain the standard air cooler on its US $2,999 ex. VAT GTX Titan Z but the price apparently is that it now takes three-slots.