Verm
3
…painfully and slowly by hand… 
Most of the errors I have found have been from GeoBase imports, but I have seen some from CanVec aswell.
CanVec errors seem to be more the nodes are placed but no “way” joining them.
Also, quite often there are errors on ways when they cross a provincial border. The ways are not joined.
a big example:
HALF of the city Nanaimo in BC was doubled up! I zoomed in and all looked fine, but many errors were reported, so… I picked a junction and drag it away… and second set of ways was directly beneath from an earlier import. I did a lot of cleaning up. I noticed a couple of other mappers had found the same thing and were cleaning up aswell.