One of the deceptions is going by CAS (or CL) only, and ignoring the other memory settings, because they are just as important to performance too, which is why I don't care for "regular", "premium", or "super premium" labelling. A stick with a CL2.5 2-2-5 1T timing is unquestionably better than CL2 3-3-7 2T timing.
The most important factor in buying memory, I think, is going with a name brand, such as Kinston, or Crucial, because they offer and stand behind lifetime warranties on their memory. Kingston, for instance, I haven't had to return memory to them, but I did return a network card once, and they replaced it, sent it back to me fedex 2-day air which made the shipping costs more expensive to them than what I paid for the card! That's great warranty service.