Honestly, I haven't felt compelled to OC video-cards, even under my most extreme usage.
I used to compete with benchmark builds. Back in 2006, I built a custom 8800GTX SLI build with an X6800. During the old ATI 9700 days, I built a 9700 Pro system on an Athlon M motherboard with water.
I used LN2 on a few builds too.
Most times, there's much better scaling pushing the processors than video-cards, so I don't really frown or think much when people don't OC video-cards.
The thing about video-cards compared to processors is that video-cards really have to launch at as close to their max performance as you can get. Binning usually means cut features which has nothing to do with clock speed being the deciding factor. The reason for this is because discrete graphics is a very niche market, so the mainstream and low-end market are still enthusiasts which means you can't afford to cut corners. With processors, this isn't the case. A mid-range and low-range user might not use games or 3d graphics so they won't notice the difference between an E5300 and an E8500. Think of a Core 2 Duo E8500 as a GTX260, and think of an E8400 as a GTX260 that's clocked 75MHZ lower. Exact same chip, exact same architecture, but lowered speed, lower cost for a user that won't notice. But if you notice, with video-cards, that isn't the case. A 9800 GT varies greatly from a 9800 GTX in architecture and performance, even at the same clock speeds.
Of course, 5 or 6 years ago this wasn't the case. Before laser cutting and unified shaders, some video-cards had less features because of their BIOS and clock speeds, so a simple BIOS flash and a nice cooler was the difference between a 9500 Non-Pro and a 9700 Pro (The good old days).
With processors however, bins are so different that processors will often ship as high as 100% under their max clock, so you can benefit greatly from over-clocking them. The difference in performance does not lie. The most I've seen out of a GPU over-clock was maybe 5-7% performance increase, and it never made an unplayable game setting change to playable. It just made playable a little better, but that never meant noticing a difference.
The limit for me as far as video-cards goes, is maybe a 15 MHZ increase and better cooling. Any further than that, and the added heat, power draw and risk of failure weighs more than the gain in performance.
