In my opinion, overclocking is useful as a hobby and if you are curious to see what you can get with a minimum of trouble.
However, you should not rely on it to give you a CPU which you NEED to do real work.
The time messing with cooling, heatsink compound, different fans, voltages, and making sure that it's completely, 100% stable can add up. If you are already being paid to mess with computers all day at work...well, you can do the math. In any case, there is no guarantee that your 900 MHz proc will work at 1 GHz, even if everyone else's seems to.
Also beware, it seems that a sizeable group of overclockers are willing to live with "mostly stable." I had a CPU which would run 3dmark all day at a very high speed, but there was a large margin in which every normal benchmark would run, but Prime95 would reveal rounding errors, etc. It seemed to work fine for Quake, but if I am writing a mission-critical program, I don't want to risk that error.
In all, it seems that there is a fair degree of "optimism" when it comes to o/c'ing reports.
My suggestion is, if you need a 900 MHz CPU for something important, then buy a 900 MHz CPU. You will be assured that it works. If you want to o/c for fun (it is a lot of fun, I admit) then do it in your spare time.
If it's a gaming machine, then by all means clock it up to the breaking point.
And yes, a 750 Duron seems particularly eager to o/c. Before you make a final choice, also check out the prices for cheap Athlons, right now the lower-speed T-birds are incredibly cheap!
Good luck!
oms