This may have already been covered/discovered, but I stumbled across it last night.
It has always been a pain A/B comparing tracks: hit the solo button for the A track, then quickly toggle off the A track solo button and hit the B solo button. There's that lag thats not just annoying, but it gets in the way of a good instantanious comparison.
So here's what to do. Hit the solo button for the A track, but leave the one for the B track off. Then right click one of the solo buttons, select Group/New and assign a group to it, coose a color and all that. Then right click the solo button of the other track and add it to the same group.
Now all you have to do is click either solo button to make the solo track change between them instantly.
Forgive me if this has been covered, but it bears repeating anyway.