I got my G2M yesterday and after an hour of messing with never could get it to work. It had horrible latency, missed notes all over the place, and I'm a very experienced guitarist with good technique. I really thought it might have been my unit. Then I followed the instructions very carefully and did a few things listed below and was blown away by how well the G2M actually worked. It now gives me very low latency, almost undetectable on the treble strings, barely there on the bass strings and no more missed notes if I'm playing clean. Here is what I did, good luck everybody:
1) First my equipment: Fender strat with stock pickups (yeah I know I'm one of three people on Earth still using stock pickups), neck position with tone and volume controls wide open. G2M on boost going into a MIDISport 2x2 and from there into a MacBook Pro. My audio device is an Apogee Ensemble and I tried this with various standalones (Analog Factory, Ultra Analog, Absynth, Massive) and with Ableton Live.
2) Get your axe in tune. This seems to be the single biggest factor in getting the G2M to work. First use an electronic tuner and get it zeroed in perfectly. Then use the G2M tuner to get the green light solid. Be patient. It's amazing how precise it is, but when your guitar tuning is zeroed in with the G2M, you will have a whole new experience of this device, I promise.
3) Use the G2M boost switch (slide it to the right) and make sure you're not constantly clipping. Some clipping is okay and I think it is even necessary for this to work right.
4) If you have multiple MIDI devices, disable all that you aren't actually using. In Ableton Live MIDI Preferences I had about five MIDI devices enabled that I was not using.
5) OK now test by using a simple sawtooth synth. You should now have virtually latency-free, pitch-perfect tone and should be able to do pretty fast lead runs and vibrato without weird artifacts.
Good luck, I hope this helps somebody out.