brilliant guide, was just reading it out of interest, because even the best players can find something to learn from reading the basics laid out in a clear concise format.
i think you should mention that groups made mostly of more experienced players will forgo a kill order in preference to assuming that the dps, especially in a game like this can coordinate (or in some cases like my BH have amazing burst damage, who therefore pick a separate, but lower hp target which can often be taken out long before the mob has time to reach you, let alone deal any significant damage.) on the mobs without targets, meaning they won't be assigned and perhaps the best advice in these situations would be to observe the order the other dps is taking or if in doubt request. also, in this case targets may be assigned for only the hardest encounters, being explained before each time they are used (as number of mobs in these situations may vary)
i dislike this comment, as, as a more experienced player i often find creating my own build is more effective than using an "optimal" build, as these builds often assume perfect reflexes etc. and have often got gyp in "that other mmo" (most of my mmo experience comes from wow, and is the place i found players most willing to be asses for someone not playing exactly as they expected) for using a "sub-optimal" spec, that soon showed that my dps was leaps and bounds ahead of a higher level, better geared player who had an "optimal" spec (in one case i even took over tanking at one point when the tank went down and healing at one point when the healer dced, all in the same spec. (meh holy paladins levelling in cata, whatcha gonna do?)). often the best advice i can give for specs is, instead of going online and finding an optimal spec, ask more experienced friends or guild-mates who you play with, who often have a better understanding of how the talents work, while being aware of how you play allowing for a more optimal build for YOU. (this is especially apt in situations where say a spec has threat reduction, i may recommend that talent to a friend who has issues with threat, while another friend who manages it better would be steered away from choosing it.
just my 2 cents