If a car pulls out in front of you (and you have to brake hard to avoid hitting them), then procedes to do 10-20 mph under the speed limit, I can see getting pissed off (I know I do... it happened yesterday and I got pissed off.) Driving slow in the left lane for no apparent reason is proof that you're either an asshole or completely oblivious to your surroundings and shouldn't be allowed to drive at all. With a few exceptions (heavy traffic, merging traffic, etc.), the left lane is for passing, not travelling. If you're not passing the car on your right, either speed up or slow down, but don't go the same speed. And for gosh sakes use your fucking turn signal! They should issue stiff tickets for "lane violations".
As for biking, even on backroads, I rarely see more than a few cars built up behind bikes. If you're a biker, and you see that there are more than 5 cars behind you, please do them a favor and pull off the road if they can't pass you while you're moving. If people would actually stop to think about the other person for once, everything would move so much smoother. If you're the biker, think about the car, if you're the car, think about the biker.