I just spotted the "keep right" link in the wiki page for my town, and found that it's a great error checking tool. It helped me fix up a lot of small errors in my area.

For anyone who wants something to do, there are lots of highways that haven't been joined properly in this area:

http://keepright.ipax.at/report_map.php?db=osm_EU&zoom=15&lat=51.17439&lon=-0.16685&layers=B00T&ch30=1&ch40=1&ch50=1&ch60=1&ch70=1&ch90=1&ch100=1&ch110=1&ch120=1&ch130=1&ch150=1&ch160=1&ch170=1&ch180=1&ch191=1&ch192=1&ch193=1&ch194=1&ch201=1&ch202=1&ch203=1&ch204=1&ch210=1&ch220=1&ch231=1&ch232=1&ch270=1&show_ign=1&show_tmpign=0

(oh and when it complains about waterways intersecting rivers, they should be on different layers - don't add an intersecting node!)