Unfortunately there is a huge cost here in leakage. The big problem with graphene is that it has an intrinsic bandgap of zero, so that it can hardly switch. If you have access to the article you can see that the Ion/Ioff ratio is a measly three! These are more useful as amplifiers than transistors.

A big research goal right now is to engineer a gap in graphene, but no one has succeeded, unless you count carbon nanotubes, of course.

Actually, a quantum hall effect has been observed in epitaxial graphene, and the resistance quantization is four orders of magnitude closer to the quantum h^2/e than in the exfoliated "scotch tape" graphene. You need to keep up on your Nature reading, sheesh!

The real problem is that the band gap is still zero. These things have an on/off ratio of the order of 10 or less, orders of magnitude worse than Si, the material they are supposed to supplement.