Actually, this has been around for quite some time (it started in the 60's with experiments on cats!!!), in the previous link, one of the referenced studies went back 3 years later and found that all of the improvements had been sustained. That was in 2005. This site: http://www.aboutneurofeedback.com/ references the same researchers:

"Dr. Joel Lubar at the University of Tennessee and a few others have done long-term follow-up on clients. Dr. Lubar says they’ve followed ADD clients who’ve sustained their improvements from neurofeedback for 10-20 years."