My main (mapping) interest is British railways, but I am also interested in canals and mapping generally.

I use a Dell Axim X51v PDA running Windows Mobile 5 in conjunction with a Bluetooth GPS receiver. On this I run MapFactor's Navigator Free on the few occasions that I need a generic SatNav facility, home or abroad.
More often I use gpsVP and a British Garmin railway map file that I create by running a download from geofabrik.de through mkgmap (using CreateIMG.bat by Marco Certelli). This is what I then use to compare OSM data with what I see on the ground to identify edits required, along with liberal use of the Bing background in Potlatch.
I use gpsVP on my PC as well. But on the PC I also use a different set of style files to create an alternative Garmin map file which I use with Garmin's BaseCamp software. By coding railway lines as types that Garmin considers to be roads, I can use BaseCamp to quickly create tracks along railway lines between any two given points. Potentially an excellent way to create digital records of railway journeys.