This is a response to the 1st post, but most locks that I know have actually opted to level their alts and make these alts their main.
You can see lock pvp and pve ineffectiveness through the census too - both "across all servers" and on "individual servers" (at least the sampling I took). If you look at the percentage of 80 locks compared with the 70s prior to wotlk, the percentage has dropped significantly: 12% to 7%, where we are now the least popular class among experienced players (below priests and shamans). There will be a definite drop due to the addition of the DK, but we've lost much more share than the other classes.
Blizzard probably has much more accurate information, but if they are looking for empirical evidence, I would definitely look at census data.