Counting cards in Catan?
I've tried counting cards while playing Catan, and I've really found it a needless distraction.  It really isn't worth the effort to know that Player X has exactly 4 Ore, a Grain and a Sheep in their hand.  It gets much too confusing too quickly, especially when you throw in robbing and trades.

Instead, I focus only on counting my most scarce resource.  Since that's almost always the one I would try to steal or trade for, that information is valuable enough to make the effort for.  There are relatively few of that good in circulation, so keeping tabs on them as people buy, trade, and build with them is much easier.