The system looks very complex looking at it from afar, but to crows this system provides many opportunities to breed with other crows where other birds would fail. Crows are very plentiful birds as it is, and their system likely contributes to their high numbers.
I've seen many flocks of pigeons in the city. In the country, I often see flocks of starlings, and every now and again I'll see a flock of goldfinches.
If I can't get a good look at a bird, I'll likely have trouble identifying it. But I'm pretty confident in my crow spotting abilities. The contempt I hold for brown-headed cowbirds definitely keeps me on the lookout for their distinguishing traits, so I'm at least good at differentiating them from other birds.