take the time before cataclysms release to message all of the glyphers that post heavily and propose to make a whitelist group. what this is, is a group a people who all have eachother as whitelisted.
Whitelist in a Nutshell:
The concept of a whitelist is simple, you offer to add someone to your whitelist in exchange for them to add you to theirs. what this does is makes everything that you or them post using quickauction or apm the same exact bid/buyout if and only if they are the lowest in the AH.
example: Jack has a glyph posted for 20g buyout/bid and Fred has the same glyph posted for 21g buyout/bid. Now lets say you and Fred are on eachother's whitelist and Jack is on neither. If you were to go in and post the same glyph using apm addon, you would undercut Jack for whatever your undercut setting is, since he was the lowest post. Now the market is Glyph of Blanketyblank You 19g99s99c buyout/bid , Jack 20g buyout/bid , and Fred 21g buyout/bid. Now Fred comes back from questing and goes to re-list the glyph (remember you are on his whitelist) after he posts his glyph the market is now Fred 19g99s99c , You 19g99s99c , and Jack 20g. you and Fred now dont have to worry about continually undercutting eachother, you both have a shot at the sale as you are the same price, now you only have to worry if Jack undercuts you both. Then the chain starts over.
The whitelist is a great tool to avoid the ruthless battles of glyphing, alching, and other markets that require a lot of cancelling/relisting.
Pros & Cons
You will be posting glyphs at the same price as everyone on your whitelist which means that someone may make a sale because their name comes first when a buyer is looking for a glyph. I've done the comparison and i found that i averaged roughly 1-5 less sales a day when i was in the whitelist group.
Since there isnt very much undercutting anymore you will notice that prices tend to stay higher, of course most people only undercut by 1c but if you get the deep undercutters on board you can make much larger profits.
The biggest pro i think is that you wont have to constantly run back and forth from mailbox to auction house just to make sure that your post was the lowest one at the same second someone is buying a glyph. This cuts down the time you spend trying to make gold on glyphs by a huge amount.
choosing not to be part of a whitelist may earn you 20 glyph sales in 2 hours of constantly running back and forth from mailbox to AH. To make good money you have to put in that kind of time.
now say you decide to join the whitelist you will probably sell 15 glyphs in the same amount of time, but the difference is... The price of each glyph was 7 gold higher because all the undercuts didnt happen. Plus you didnt have to constantly run back and forth so you freed up more time for yourself to read blogs, make gold with othe profession, farm, run bgs, or even show up on time for that raid.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Now the reason the time to do this before Catacylsm is better than after is because once Cata releases all of the glyphers will see how much money they are making without the whitelist, they will never believe that they would do better with it, thus creating the requirement to camp the AH to fight the undercutters instead of going to enjoy the game. Showing them how much better it is with the whitelist is by far your best option before letting them recieve the taste of Cataclysm.