This should be hammered into people's heads when they learn to drive, and tested every time you want to renew your license.

If all of the following is true:

1. You are on the freeway


2. There is space in front of you -- and I'm not talking about two-seconds-before-the-next-car, or one-car-length-per-ten-miles-per-hour or whatever measurement they're using for safe non-tailgating nowadays kind of space; I'm talking about you-can't-see-the-guy-in-front-of-you-cause-he-took-the-curve-a-mile-ago SPACE in front of you


3. There are cars in a lane to your right going faster than you


4. You aren't willing to maintain a faster speed (for whatever reason)

Then you are in the wrong lane.  Carpool lane?  Irrelevant.  Speed limit?  That counts in the "whatever reason" of condition 4.  If the above four conditions are all met, you are obstructing traffic.  Get over to your right one lane and reevaluate your new situation based on the same conditions.  To not do so is to incur the wrath of the people behind you - and in this day and age of Road Rage, that could be a death sentance.

Plus, the roads will be a lot safer if everyone allows everyone else to follow the "only pass on the left" rule that we're all supposed to be following, but nobody does because the speeds in all the lanes are so dang haphazard.