Perficient, the company where I recently worked (formerly BoldTech Systems), recently achieved CMMI Level 5 certification at their development center in China using an agile methodology. I worked in the China facility just over a year ago when they achieved CMMI Level 4 and wrote about it in a previous blog post. Perficient is now one of the very first companies to achieve level 5 using agile.
I don't advocate pursuing CMMI certification unless it's a business requirement. There are many offshore (primarily Indian) firms who tout their CMMI Level 5 certification, so it may be an important factor when competing for certain contracts.
Regardless, this is a great achievement and an important one for the agile community, whether you like CMMI or not.