I use it and think it works great. There are a ton of posts on it if you search here. Within the past few weeks there have been posts about another method, "dot tuning," that is free and getting a good response too. I can't vouch for it yet. I'm not sure if the dot tuning works for Nikons though.
I'm a canon guy but its done wonders for my set up - 4 bodies and about 12 lenses and they all are better after running it thru the software. Takes the better part of an afternoon to do the whole camera bag but its totally worth it.
