Overclocking can very well be associated with instability. This is not because overclocking unstable. This is because alot of people believe that overclocking is pushing your cpu/video card/memory for the maximum benchmark. If your system finishes the benchmark and can run the desktop and a few games, that's good enough. Other people take it a little further and if you loop 3Dmark or pass Prime95 overnight then everything is fine. In my opinion, this isn't good enough. I pass that level and can still find instability. Video compression/editing/encoding is a good example. I find that surfing, downloading songs, burning CD's, playing online games, running a media player, and running Prime95 simultaneously as well as a few other things can bring out glitches even if 3Dmark, MemTest, and Prime95 check out OK.
The point is overclocking can be 100% stable and safe if you don't push it too far, but that can take some work to be truly stable.
For me it is worth it, but some people just don't like to tweak or test that much.