So some auto centers are offering to fill tires with Nitrogen rather than air. They said there are many benefits, like increased performance, better gas milage, etc. Has anyone tried filling thier tires with Nitrogen? Any benefits?

http://whynitrofill.com/

 

The only benefit is that you don't have to adjust your tire pressure as often. Also, the tire pressure won't fluctuate as much with regards to temperature.
Since your tires will maintain a desired pressure, gas milage and handling will remain at their optimum levels.