Q3 is my go to EQ, couldn't live without it, but I have a few suggestions that might make it even niftier.
A +/- octave button would be cool, as often times when notching out frequencies from iso booths there are resonances in multiple octaves. The option to both move the frequency you're currently notching up/down an octave, and to add a second notch at the frequency up/down an octave would be really cool. Although it sounds small, this would save me 5-10 seconds on every background vocal track on every mix, which would add up pretty quickly.
Along the same lines, Auto-Tracking harmonics, which I'm sure has already been requested, would be an awesome addition as well.