Live reads are just ridiculously important.
It doesn't take great reading skills to garner incredibly important information, and people will willingly give up quite a bit. There are not only the Mike Caro-type tells, but you will realize who is down to their last $200 and doesn't want to get busted, or who is stuck $1,500 and just wants to gamboool it up.
People show their cards a lot more live for no particular reason.
Live poker is very much a social game to a lot of people, and I admit that I don't always take the most +EV lines against certain people...but if you use this ruthlessly you can get a big advantage, too. you can do things such as negate positional disadvantages by talking to them. You can find out who is or isn't willing to stack pre with JJ or AK and who's going all-in with A-high or any pair.
People are much more impatient in live games...on the Internet, people are playing multiple tables or surfing the Net or watching TV. In live games, people get frustrated very quickly if they don't get a hand for two hours, which is very very common. The same guy who might fold KQs to a $2 reraise online is now putting in $75 preflop with it in a live game.
