Am I still correct to think this way? (SLI vs. non-SLI)

Back in early 2007 when I built my current computer it was commonly accepted that the only people who went for SLI setups were people looking for benchmark numbers. The games of the day couldn't really make use of dual graphics cards and PC Gamer did a test showing that some games actually performed worse with two cards instead of one. This is the same mindset I have been in since I built this machine.

I tend to only casually keep up with the current hardware and system building trends. Have things changed since I last built a system? Can games actually benefit from having multiple graphics cards now? Is it worth the added cost and heat? Is it still better to have one single powerful graphics card or two lesser cards in SLI?

This is what I have currently selected for my new build:

-GIGABYTE GA-P55-UD4P LGA 1156 Intel P55 ATX Intel Motherboard
-Intel Core i7-860 Lynnfield 2.8GHz LGA 1156 95W Quad-Core Processor Model BX80605I7860
-Mushkin Enhanced Blackline 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1333 (PC3 10666) Dual Channel Kit Desktop Memory
-EVGA 01G-P3-1181-AR GeForce GTX 285 Superclocked Edition 1GB 512-bit GDDR3 PCI Express 2.0 x16 SLI Supported Video Card
-Antec P183 ATX Mid-Tower Case

I will be re-using several of the parts from my old system, mainly the hard drives and extra fans and such. I currently have a BFG 650 Watt power supply that I can re-use if I go with a single GTX 285, I would have to upgrade it to a more powerful unit if I went SLI. I have had notoriously bad luck with every ATI card I've owned so I would prefer not to tempt fate and stick with nVidia.

Another thing that I am concerned about it noise. With the setup I currently have I've got the sound down to a pretty manageable level and I would like to keep it that way. What sort of effect would multiple graphics cards have on that?

Thanks in advance for your assistance.

if you are heart set on Nvidia and on that P55 board that steps down to 8x after you add the second card, I wouldn't go beyond a pair of 275's or 260's. both great cards.