Well I am guilty of being both a left-lane driver AND a non-signaler.. However I have reasonable reasons for both offences:

In the left lane, as someone stated earlier, I am nearly always the fastest car on the road (which may or may not be such a good thing), and pulling back and forth between lanes would be unnecessary and unsafe.

As for turn signals, I hate taking my hands off the wheel, and I'll always do a head-check to confirm that I've got space in the next lane. If I'm going to really slide into a tight spot, I'll always signal, but if I've got plenty of room and I'm accelerating past the person I'm getting in front of, I'll just smoothly change lanes.

I was thinking about a way to put turn signal buttons on the steering wheel.. like in the new Ferrari Enzo Ferrari Ferrari Enzo... whatever it's called.. I'd use my turn signals ALL the time if I had thumb buttons..

But let me tell you.. NOTHING in this world winds me up more than cruising at 88mph in the let lane, cresting a hill, and seeing BOTH lanes blocked up because some joker in the left lane thinks that it's a good idea to pass the right lane under cruise control which he has set at about 4 mph over the limit..... There have been times when I've seriously considered hood-mounted rocket launchers..

-Adam