I hate to totally disagree with what the last poster put up, but after 100,000 axe swings on Decorative Weapons in RuAvitau, I managed to parsed a +3% rate in criticals from a baseline amount I've averaged on myself through about 250,000 axe swings in sea and sky [10.25% with maxed critical rate upgrades and a gear setup with about +30dex]. Ok, so it was actually +2.98%, but that's close enough. Experimentation was done swapping this earring with assault earring, in conjunction with a Suppanomimi as 75WAR/NIN. As close to 50,000 swings with both as I could get. All other gear was left the same and the same food (Sole Sushi) was used 100% of the time. So, either Sole Sushi (as opposed to any other kind of sushi) has a hidden +3% criticals effect, what else would you attribute it to?
This same conclusion has been reached by others I know... parsed but without the exact same scientific method to record it that I used (they reported anywhere from 2-5% increases from what they thought was normal for them, but during the course of only 1-2 PTs).
I'll agree with everything else from that post, however. 3DEX, is, well, 3DEX. 2DEX = +1acc in +stats, there's no mammoth accuracy gain with this earring, etc.