I have one on a Carvin Bolt. Installed by Elderly (I work a mile from there), who recommended them highly and keep them in stock.
No complaints, no problems. I can't say it helped the tuning much, but Carvins seem to ring truer because of their CNC and fretting processes (might be urban legend, but apparently Buzz Feiten told Carvin that they didn't need his system for these reasons).
This came off another guitar that I sold and I kept the Earvana. The other guitar had a Warmoth neck - the Earvana helped that a bunch!
I have them on both my electrics - a Walnut "The STRAT", and a '62 Reissue Tele Custom. I love the Earvana nut - it's made great improvements in my intonation. High triads ring truer. It's ALL good.
I had one on a Les Paul I used to own. I agree with oxtone. Everything rang truer. It really did make a big difference. I would highly recommend the Earvana nut as well; just make sure a highly qualified tech installs it so it performs as advertised.
hmmm.. this must the holy nut grail or something if everybody likes it. Yes I did use the search function and found some 'non-believers' in some of the other threads, just thought I'd check and see if anything has improved. I've got a strat, as-93 ibanez 335 clone, and an LP that all need work done to them, I thought I'd go ahead and possibly replace the nuts in them if I thought I could get an improvement in intonation.