I bought the revised editions of the Core books, and I am happy with them, and with most of the changes that were made.
I also, as some others, own Many (over 30) of the D20 (3.0) books- from Forgotten Realms (all of them), to the AEG supplements. Yes, some things are changed, but I would think that would be expected of a "revision." I do not see nearly enough changes to the system to even consider these to be considerable as a new edition, and here is why:
-Rounds work the same- what you can do in 6 seconds you can do in a round, (better than the previous, absolutely ludicrous 1 minute rounds)- there are still full round actions, standard actions, free actions, and move equivalent actions. Only partial actions are gone for they were redundant, and the system in no way changes with there absence.
-There have been very few changes to the races, and the very insignificant ones that were made, fit completely within the same system
-Class abilities have been altered/improved where they needed to be, and still fit perfectly within the same exact system. I am still using base attack, and getting a defined bonus determined by the class I take, I am still using Fort, Ref, and Will saves, bonuses again being determined by the class I take.
My experience chart is exactly the same (still for all classes/multi-classing/prestige classes- which are also still a part of the system
The flow of combat remains the same- I roll spot (determine if there will be a surprise round), I roll initiative at the beginning of the first regular round, and I will go again on that same initiative count each following round (provided I don’t use a delay action, or some other SAME mechanic)
I still benefit from any Feats I may have for the combat (which I still receive every 3rd level), I will still attack using my Base attack bonus +ability mod +enhancements, and the DC will still be the AC of the creature I am attacking. I can still threaten a critical, differing for what weapon I may be using.
Some creatures are still immune to critical hits.
Ability score damage works the same way (and some things are immune)
I still compare my level to the CR (EL) of a monster/encounter to determine experience awarded.
I still take a standard action for casting a spell. Concentration checks are still required for certain circumstances.- Oh, I still gain a certain number of skill points per level, determined by my class, and some skills may still be cross class, and my max ranks in a skill are Still my character level +3.
I still need a feat to make magic items, I can still use metamagic feats to alter my spells

eek: and alter the levels of my spells- a good argument as to why the changes to some Spells' levels were merely insignificant, while entirely necessary and beneficial)
I can go on and on listing all the information on Why this system is exactly the same, but I really don't need to.
If I have played 3rd edition D&D, and know how to make a character, what Base attack is, what Saves are, what feats and skills are, What AC and Initiative is, how the combat round works (actions I can being full-round, standard and move, etc.), and how all this works to make the system, then I also know Exactly how the revised edition (3.5) works.
THAT is why this is D&D 3rd edition Revised, NOT 4th edition.
Oh, and I must add, this: The fact that you play a D&D game, no matter the "format" (Living Greyhawk or what have you), you are in NO WAY forced to buy the revised Core rulebooks (anymore than you are Forced to play in Living Greyhawk). Secondly, even IF you, for some psychological dilemma, where not able to stop playing in Living Greyhawk, you are Still not required to buy the new books for the availability of the SRD.