The Cincinnati Bengals ran six offensive linemen formations on 6.6% of their offensive players in 2010, according to Football Outsiders, which ranked fifth most in the NFL. That's a slight decrease after leading the entire NFL with 86 plays from six linemen formations in 2009.
Many teams still only use six linemen in short-yardage situations, which we also call "power" situations. For example, Chicago used six linemen 11 times, all in power situations. So in our table, we've also listed how many plays a team used six linemen in a non-power situation, and how many yards per play they had in non-power situations. We also list how many times a team ran a pass play (pass or scramble) from a 6OL set.
You can see their table here.
The Bengals often used Dennis Roland as their sixth offensive linemen, noticeable because the beasty would go into motion, which wasn't too dissimilar as noticing a 60-year old ninja riding a bike and ringing his handle bell. Actually, you'd never see him. He's a ninja. Even when Roland was playing a majority of the time during certain games, he often shifted outside to the tight end spot.
Yet the six-man offensive line wasn't useful to the Bengals in 2010. According to the same chart, the Bengals only averaged 3.0 yards/rush with a sixth linemen -- and only 3.8 yards/rush in non-power situations.
In a totally unrelated note that has nothing to do with anything, Dennis Roland and Nate Livings are free agents.