Hi.
I want to bitch and moan too

For me, the only moments I did really enjoy WoW were the levelling part when I did it for the first time (have 7 lvl 80 char atm, so this gets me bored as well now ^^ even tried Dual-boxing to "get some new fun in the game" and I must admit it was fun... 3 months ^^) and everytime I have been able to play with a full raid of people of equal/similar gear and skill than me.
The latter is basically what gets me frustrated and sad at the moment, as it is sooo rare that you don't have to carry a couple of people through a raid. Honestly, I prefer raiding with 22 raiders fully involved and 3 empty slots than with 25 out of which 3 don't care and have to be carried through by the 22 other people...
Really I have no clue how this could be implemented (it probably could not cause "skill" is something hard to evaluate) but I'd like to have skill-based server population, a little bit like there are several levels in Sports. Only the 20 best teams can compete for "first division championship" (whatever it's called in your country : Premier League, Div ProA, ...), then the 20 next compete for championship in "second division" etc...
I'd love to see players offered the possibility of moving to a higher level server, and gently offered as well the possibility of moving to a lower skill server when there is a too big difference in skill with other players from the same server.
This would ensure that you have a greater chance to really being at a challenging point in WoW rather than either lacking far behind your guildmates and still pretending you are a HL-player just because you killed Jaraxxus in Hard Mode (OK, you were behind the tanks in damage despite being a DPS-class, but still you were in the raid when he died...) or having to constantly compensate for guildmates pretending they are End-Game players but have to L2P...
As well, this would give GUILDS a better chance of finding the players they need when they look for some new members.
Not sure if I did explain my point properly... but yeah... would just be great if everybody with same skill would be together

Obviously from above, the answer to OP is same as HoHo : Always ^^