±0.1mm tolerance is a typical value for a lot of suppliers, and from what I have seen they often advertise the same error margin for both 1.75 & 3mm filament. Keep in mind that given the same millimeter difference, the percentage error is doubled for 1.75mm filament compared to 3mm. This might be a point to support plexus' for using 3mm filament.
Protoparadigm has an in-depth article on the subject of filament tolerance:
http://www.protoparadigm.com/blog/2011/ ... t-quality/Incidentally, they advertise a .05mm tolerance for their filament (both 3mm & 1.75).
But to answer the question… I have not run into any significant problems that I could attribute to filament tolerance. In general, unless your machine is exceedingly well calibrated, other errors and small inaccuracies in positioning and repeatability are going to be more significant.