The bubbles of nitrogen are a lot smaller than co2 bubbles so it gives your beer a creamer taste and mouth feel. Notice the next time you go have a pint, look at the co2 bubble and then get a guiness or something on nitrogen and look at the bubbles in that beer.
Some micro brewers use a certain amount of nitrogen when they are carbing up there beers. They will hit the beer with nitrogen for some time, and then co2. The smaller bubbles of nitrogen make carbing faster, but also give them some lacing and head retention.