I always read every answer choice, but not with the same level of focus and attention to detail.
This is because many times on LR and RC problems, there is an answer choice specifically designed to be confusing and drain your time - if you stare at it and try to decipher it, you will often lose 30 secs. to a minute, just on that choice. So if I have an answer that I already like, I will usually not waste time on this type of answer choice, and just proceed. I will, however, mark the question for review - by forcing myself to make quick decisions, I am always left with ~5 minutes at end to review these types of questions.
I call these answers 'time sinks', and I avoid wasting time on them because that is what the test makers want you to do. If, however, I've gone thru all five answers and nothing pops out, then I find that its usually that damn confusing answer that I need to pay more attention to. PERFECT EXAMPLE: Car theft question on October 2010. "Abandon" was the uber-complex answer that turned out to be right, which I chose in the end.
In addition, I never read all the answers on identify the main point and sufficient assumption (justify the conclusion) questions. There is always one correct answer, that can almost always be pre-phrased, and there is literally no reason to do anything but a quick skim of the rest.
Also, on parallel reasoning questions that lend themselves to a clear diagram, I usually pick first answer that fits. This takes practice to recognize correctly, but you can save a lot of time here once you get good at this.
Overall, as you practice more, you will find you can get away with a lot of quick skimming of answers, on MOST problems (but not all). Your intuition gets refined and you start to anticipate exactly what test makers are looking for. It took me about ~15 PTs until I finally started to feel this.
My PT average is 176. Felt great coming out of december, except for LG of course.
Hope this helps.