I find that I check my tree quite often. Every time a new bit of information - dates, marriages, siblings, etc. comes up I check through. From time to time I'll formally add census records etc., and i really must admit I'm very suspicious of a lot of other trees I find that seem to have adopted my rellies in, and often merged 2 or 3 sets of different children ... I mean, I know families were a lot larger, but I'd expect them not to have two different "same first name" siblings, both growing up! I'm used to re-cycling of names of dead children, but you'd think some of these compilers might suspect it was a bit odd to have to call two "Same first name"s in each evening?
And I agree; just because I think I'm correct doesn't mean that essentially I am more correct than anyone else.
It's actually quite fascinating where you do find you've found a mistake in your work, it leads you to re-check everything leading in both directions.