My breaking point came for two reasons:
1) As an official mouldy relic (age 65) I started with the original 3 book set. Since then I've bought a tremendous amount of 1.0, 2.0 3.0 and 3.5 compatible material. I have shelves of the stuff. What galls me is when then one gets sold the same content, just updated for the current version. I have enough stuff to last me twenty years, probably long after I depart from old age. I'm not paying for the same content again. And worse yet, 4.0 is not backwards compatible.
2) I really liked the 2.0 rules but understood the need to go to a rule set that is computer gaming compatible. Its the world we live in. I play games on-line and have made my living since 1967 in computers, even before it was offered in college. But I believe that the 4.0 system has taken a lot of the fun out of the game; if you want to play like a computer, go on line (just an old guys personal opinion). Our group, formed in 1983, just switched to 3.5 from 2.0 in 2007, mainly because several members were heavily into Never Winter Nights web design. I don't think we'll be switching again.
I did buy the core 4.0 books to see if I liked them. I won't be buying any more 4.0 products; I'm going with 3.5 compatible products along with D20 stuff and generic role aids like miniatures, flip maps, Dwarven Forge stuff, and other role playing aids. At some point one just has to say no. I do like the Pazio stuff a lot though and continue to keep them "green". 8>)