Hey @phillysteak527 (over at Local Motors Projects website), I use the positive photoresist method to make my PCBs and I can get tolerances finer than that photo above without any issues at all. It's super easy. I often run traces between the legs on .1" headers and even on QFN and QSOP packages. Between the silly-sharp quality of my cheap little Samsung B&W laser printer and the photoresist process, the accuracy is amazing. Take a look:
I draw everything in Illustrator, mostly for the enjoyment of hand-routing the traces and also for the ability to make the boards more artsy, otherwise there's no practicality to it. ;) I tend to make the signal traces 0.5 pt wide (a hair more than 6 mil; 0.5 pt is a quick selection in the Path toolbox in Illustrator). I prototype this way because I can draw rapidly in Illustrator, print on paper and dry-fit the parts to make sure they fit, then print on transparency, expose and etch in minutes. No waiting, especially if there are mistakes.
But, if I ever got to the point where a project was viable enough to make multiple boards, I'd most definitely go the OSHPark route. Take this project, for instance... Once this bad boy is back up and running and the boards are doing their jobs well, I'd like to sit down with you and work out the most efficient way to lay all this circuitry out for modularity and, of course, fire and electrical safety. ;) I have a complete system map laid out to make visualizing the modules easier.