I tried S-voice, but it kept activating when I was having skype calls for my work (on my laptop), so I had to disable it. I definitely wasn't saying "Hi Galaxy", but maybe I just talk to quickly and the voice reco got confused.
I agree, the S Voice triggers accidentally at times. Especially during making videos when I have to say "my galaxy note". And sometimes rarely when I say words that sound nothing like it. During skype calls would be really annoying for sure. Even with the few accidental triggers, experience for me has been overall positive.