Yeah, I think OC'ing is mainly just a "see if I can do it" type of thing. I'd only really OC the CPU on old machines, 386s and the like, where I dont care if I burn up the CPU.
OCing the fsb is a little different, but then again you can't get much just from that alone. Not to say that the fsb cant be a bottleneck, since it can.
What makes the cut really is RAM lat, HD speed / cache size, CPU cache size.
I have OCed processors in smaller devices (eg Palm) but those are a different story since many of them are designed "scalable" -- low clocks, higher batt life, high clock, lower batt life
The Palm I use right now is the PalmOne Tungsten E, with a TI ARM OMAP311 cpu.
Factory settings, clock it at 126 Mhz. I've OC'ed it to 172 Mhz for doing stuff like watching movies etc, though I try to limit how much time is spent running OC'ed and am overall really cautious. TI says 172 is the max you should bring an OMAP311 up to, I dont go higher even though the OC'ing software it uses can bring it up to 185 Mhz.