Most RepRap vendors advertise the smaller nozzle sizes (such as the 0.25 mm bore) as being experimental. This is because it requires a finer tuning of the printer and slicer to achieve good results. There's also a higher occurrence in extruder jams with the smaller nozzles. We're going to run a series of tests using the 0.25 mm nozzle to print the 0.2 mm and 0.1 mm layers using a 3 mm filament.
Registering a bore size in Skeinforge is not a simple task. It requires you to calculate a ratio for each layer of a different thickness. Following the steps in this recipe will help you understand the process and make it easy to make adjustments for any change in the nozzle size or print layer.