In my experience if the application is simple reticules work well. The more exotic the application, such as projective stereo measurements, they work less well. Usually a reticule is place in the right eyepiece since, in most heads, the right eyepiece doesn't move. This means that only the right eye sees the reticule and the image. If you look closely though a microscope with a reticule in the eyepiece you can see the image through the reticule.
Some people use two reticules, one in each eyepiece.
This drives me crazy. Reticule will never line up perfectly center to center. This lead to an unacceptable amount of eyestrain as far as I'm concerned. If you need a specialized reticule they can be made by several very good companies for not a lot of money. In fact there is such a range of reticule made by reticule companies that usually you will find what you want in stock.