I'm personally a bit of a big time overclocker... I spend HOURS upon HOURS getting the highest stable setting that I can get.
I recently upgraded the PC and Graphics card, the card isn't the best available but it's the 8800GTS which is pretty respectable. That's overclocked by about 25%.
The biggest overclock is to the CPU and RAM. My CPU Standard was 2.4Ghz it's a Core 2 Duo E6600 which I've put a Thermaltake Big Typhoon on, one of the biggest air based coolers you can get without going to water cooling. I've cranked it up to 3.7Ghz which is a 54% overclock.
With the overclock my 3D Mark 06 scores went from 7771 to 10913 which is a HUGE gain for this graphics card and processor setting, so I was majorly happy with that.
SuperChunk - there isn't anything to worry about with overclocking, it's probably not something someone who doesn't know what they are doing should attempt, but if you know what you are doing there is relatively 0% danger on current PC's as most boards are built with some form of Overclocking in mind. As for the minimal gain, I beg to differ, the 'feeling' of my PC has increased by a huge multiplier going up from 2.4Ghz to 3.7Ghz... In the past CPU's might only just go up by 200 - 400mhz MAX but whe you can pull a 1.3Ghz benefit, the thing just SCREAMS along.
That's just the feeling in Windows, in games things like Company of Heroes which is a pretty hugely taxing game has gone from a barely playable 18fps at the best settings, right up to 29 - 43fps for most of the time... that's a pretty significant gain I think and I believe i can still pull more out of my Graphics card.
The gains are good, but I also get a massive amount of enjoyment out of modding, volt modding boards, building PC's and cranking the absolute max (RELIABLE) power out of it, it's a bit of a hobby and a past time of mine.
Next project is creating a Home Theatre PC that is in-audible using ONLY case fans... that's probably going to require under clocking and under volting the board to a good acceptable level and using a fanless GPU, there are lots of obstacles to overcome with that project, but it's still a hell of a lot of fun :D
