I'll agree, but online is only a little different. The physical
tells aren't there, but there is a lot you can pick up from watching. You can pick up betting patterns and classify the player (Tight, agressive, passive, loose). Also if you take enough time you can see how often they
bluff, and what amounts they like to bet when they are
bluffing. People are creatures of habbit, they like to repeat. It's a good exploit.
However, big NL tournaments, play the odds. Unless you get down to the final table or two, there isn't enough time spent with any one player to pick up on anything. But once you're at that final table, I'd watch close because the rewards are huge if you can pick something up.