I have my Feline Lion set so the Mules are out of phase when they are both selected.
It becomes very thin and scratchy sounding. If you mute with your left hand and strum staccato with a pick you get a quacking, scratchy sort of wah wah type sound. Can sound quite nasal
It sounds great clean tone for funky stuff but I wouldn't use it for blazing leads any time soon.
If you roll the volume back to 8 on one pickup and leave the other on 10 things seem to go back in to phase. So if you roll it back up it then jumps out of phase again which can be useful.
http://uk.youtube.com/watch?v=VpQBasKrUpM&feature=relatedThis is a good representation; the guy rolls the volume back and forth on the treble pickup between 43 and 56 seconds in the clip. You can hear when it goes thin that the pickups are out of phase.