Update: Forget about small details, NDAs have been lifted and complete information on NVIDIA's GeForceFX 5900 Ultra and its main competitor 256mb equipped Radeon 9800 Pro is now available.
Even some of the bigger sites seem to be hit with the massive attention these articles are generating, here are some of the articles I could actually access by time of posting: Anandtech, Hexus, HotHardware, Neoseeker.
Both CNet and VRZone have posted information about the GeForce FX 5900 card that will be officially announced later this week and is based on the NV35 chip.
According to the first article, FX 5900 boards will go on sale this June, priced around $399 for the regular version and $499 for the "Ultra" version with more memory (probably up to 256mb, but will it really make a difference?), I'd assume faster clock speeds are expected for Ultra as usual. VRZone also has details on memory clock initially slated to run at 425Mhz, was later improved to 450Mhz with the latest card samples.
Also, from those leaked pictures it'd seem that NV35 boards would use two slots like in FX5800 boards but that's not the case, NVIDIA says they expect to have all shipping boards using an improved cooling system that will take a single slot.
NVIDIA is also expected to release a new set of Detonator drivers that will improve performance considerably along their entire FX line, hopefully that will remain true in terms of real optimizations and not visual quality tricks, 5200 & 5600 boards would become a lot more attractive with a 10% performance boost for instance.