Rizen just wrote a great article on P5's...

[uclabruinz]

Playing unexploitably vs optimally is a great topic for discussion. From NLHTP:

"No matter who you are playing, the fundamental remains the same. For every play, try to think of what the perfect strategy [Paul: "unexploitable"] might be. Then adjust that strategy to capitalize on your opponents' weaknesses [Paul: "optimal"]. Be aware of how your strategy deviates from an unexploitable one, and watch out for opponents who might be trying to exploit your mistakes [Paul: so you can exploit their effort to exploit you]."

Online when multi-tabling I tend to shoot for unexploitable early and optimal late. Live I try to lean more toward optimal, but am willing to shift to unexploitable at tough tables.