Despite the warnings in the past, there are always a few people who click on that "update" button before checking to see if the new Web Driver is out. For most folks I would guess that the Web Driver will be out in 24 hours or so and they should just wait.
If you have already run it, the GOOD news is that once again the EFI cards get a major break. You still get screen output in 10.10.5 post security update withOUT the Web Driver. The bad news is that there is no official route to have accelerated display, though I am certain Nvidia will have a fix out very soon. If you have already updated, here is a fix that will get you back up and running. Note, you will have to run in kext dev mode.
1. Run the 10.10.5 security update of 10/21/15
2. When you restart, if you have a card that requires Web Driver and has EFI, you will see laggy, unaccelerated video. (Black lines marching up the screen)
3. Go into System/Library/Extensions and drag the NVDAStartup.kext to your desktop twice. This will create 2 copies of it there. Let the system rename 2nd one. (Save both)
4. Right click to see contents of one without "2" in it's name. Open up the info.plist in X-Code or a plist editor.
5. In the field that has "14F27" change this value to "14F1021". Now save it
6. Use a kext utility to install the kext. (Kext Drop works, as will most others)
7. Run "Repair Permissions" on your OS install drive. You should see that kext get fixed.
7. Go into Terminal and type "sudo nvram boot-args="kext-dev-mode=1 nvda_drv=1""
8. Reboot and you should have working Nvidia acceleration. This was tested with GTX980, should work with other "web driver only" cards.
Keep in mind that you are running with kext signing requirement off. This isn't ideal but as I mentioned, this should only be necessary until new update comes out from Nvidia. I advise again that most people wait for the real driver, but for those who ran the update already, this is a way to keep working in 10.10.5 without reverting to older OS version.
If somehow you bugger this up or if when the new driver comes out it won't install, remove the "2" from the copy on your desktop and start at step 6 above and follow to end to get back to pore-modded state.