Actually you would see skew no matter what if you look at board cards. It would be relatively small and I can't guess the direction without more thought.
In some games a flop is almost always seen. In some games a preflop raise often takes the pot, in those games there will tend to only be a flop when multiple players have higher than average ranks in their hands and you will see lower than average cards on the board. There will also be some flops that tend to make the hand end early and deal no rivers. Without looking at any data I would guess than flushes come in a little bit less often than simple analysis would predict because the turn and river are more likely to be dealt if two or more players are on a flush draw, partially blocking each other.
edit: If you just looked at a tally of every card that ever appeared that would be correctly distributed. It's just if you look at "river cards" or similar specifically that there will be skew.
I have a theory that live games without shufflers have slightly more aces come on the board than would otherwise be dictated, because the winning hand has an ace more often than any other card, and usually the winning hand is scooped up last, putting it on the bottom of the deck before the shuffle. And in standard "riffle, riffle, box, riffle, cut" shuffle, the bottom card ends up being somewhere between the 20th and 30th card a much higher percentage of the time than other locations, and in a 9 and 10 handed game, 4 or 5 of that 10-card range are the board cards. Thus aces should come out more often. The problem of course is that in situations where the ace is there, people are less likely to HAVE an ace, and thus the hand is less likely to see a flop to begin with. But I still think that even with that side effect, aces still show up on the board some tiny tiny amount higher than would be dictated by true randomness. It doesn't matter though, since any time I'm actually in a live game without machines, I am just watching the dealer shuffle anyway, and using my shuffle tracking skills to attempt to know if the card is going to a certain player or is likely to come up on the board. Knowing that the 6c is probably going to be coming out on the board much more often than it should (not for certain, since there is obviously an error rate in my tracking ability) is really useful when you get dealt red sixes.