The real question here is.. "Why not?" 🙂 I've had a Celeron 800@950mhz and (2) K6-3+ 450's @ 550mhz for about a year. Sure it's not *that* much, but if it means I can get faster FPS in games, have more windows open, compile linux kernels / programs faster, or be able to do multimedia-related stuff quicker, then there's really no reason not to. I've only had one bad experience with overclocking.. and I'm sad to say that was on my main machine -- I bought a MSI KT7-Pro2a off of someone here on Anandtech and it worked fine for several months, then started flaking out.. the Thunderbird 900@1050mhz I also purchased off the For Sale forum here never really ran at that speed -- so I only had it overclocked for a little bit. The motherboard is currently RIP, I'm not quite sure why, but I don't even think it was relating to any of the overclocking. I'm happy to say the Thunderbird is currently living in a new machine =)
Anyway.. it just depends on the type of person you are and whether you care if it might shorten the lifespan of your CPU from 5yrs to 3yrs or something like that. There's no guarantee that non-overclocked cpu you're currently running is going to live out it's life expectancy.. and neither is there a guarantee that overclocking WILL shorten the lifespan. As long as you're careful doing it and make sure you're using proper cooling (heat is the #1 killer, as I'm sure you've read many other places), you should be fine.
Servers, on the other hand.. well, I think I'll hold myself back and not overclock them =)