I agree with Lisa here, I think it's very common to drivers to perceive cyclists as Slow, no matter what speed they're actually moving at. It would be very interesting to see if this happens less to riders that "look fast", in team gear, matching helmet, agressive riding position, road bikes, than with more "anonymous" bike riders.
I also think that cyclists are just a bit too few sometimes, so we just disappear. Drivers look for cars (this is a common problem for motorcyclists too, I think), they are aware of cars, and they maneuver in traffic with cars in mind. I think we're at risk of being passed and then forgotten, as just a "minor blip" in traffic, not as a steady presence.
It's hugely annoying, though. I have saved my skin several times by just assuming that any vehicle directly ahead of me can brake or turn to the right with no signal at any possible moment. Had some very close calls before I started assuming this on a regular basis, though.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett