Spreading the dropouts is something I'm considering too. I've got 27" wheels (of course), which are fine most of the time, but I'll be adding a generator hub soon and would like to be able to add the wheel to other bikes if the need arises, and they are all 700c. I could just relace to 700c rims, and I might, but if I'm gonna relace the rear wheel anyway, I'd prefer go ahead and upgrade it (at least in terms of being able to use 9-10 speed cassettes) at the time instead of relacing again later. But that leads to needing to upgrade several other parts as well, including the cranks, chain, shifters (?...they're friction so they might be ok), etc. I'm not sure yet what I'll end up doing there.

That being said, I have spread the dropouts on a bike using Sheldon's method (a ladder, a long 2x4, and leverage) and it worked great. I just used a string to get the alignment as close as I could (per Sheldon as well). I did a little at a time and had to bend out a little, then back in slightly, and so on until it was just right. I did that on an old clunker so I wouldn't have to worry about it if something went wrong. Below is the bike I started with and how it ended up afterwards. I really just wanted to do it for fun, and it turned out really well. It's a low quality frame, but it shifts great (it has 9 speed Shimano 105) and rides super smooth. In fact, of all my bikes (and I have steel, aluminum, titanium, and carbon bikes) only my full carbon Aegis Aro Svelte rides as smoothly as the Free Spirit. Obviously, the after picture of the Free Spirit is before it was actually finished, but you get the idea.