However, the ball socket of the slizer era is remarkably more resistant than the bionicle ones. Specially the most recent equivalents to that piece have gotten cracks from just playing. For example, One of the joints used in Skirmix's hip, has cracked just from posing it a few times a week... Many other of my ball joints from bionicle era have cracked already, since it is the ball socket that gets ruined, they become unusable.
As I have been focusing more on the minifig side for years and haven't build extensively other than the initial build of a bought set, I don't have any broken bricks. I haven't noticed any stress fractures either, except for one white brick that fits in a new Kingdom's white horse. I don't know if it came with the set to use when the horse isn't wearing a saddle, or if I pulled it from my collection.
As for Bionicle, I cringe every time I pull apart the ball and sockets. It sounds like a crack every time. Nothing has broken so far, but I can't help but feel like the next one will be the break. And this is coming from someone who has confidence in Lego product quality.
In my 20+ years of collecting (even in the dark ages I bought a set here and there), the only problems I've had with quality have been discoloring and loose minifig joints. My brother and I were rough Texas boys with our toys, so Lego vehicles found their way outside in the elements often. We broke some pieces, but it was from hard wear and tear and mean cousins!
As for the minifigs, I am constantly exchanging body parts. I have noticed that most of my 80's and early 90's torsos have loose arm holes. Many of the legs from that time period are also loose; again, probably from constant switching. I can live with that because that's not so much a quality issue. I mean, they can't last forever if you play with them enough. One thing I just thought of: some arms (it always seems to be the white of light grey ones) crack from the hand to the elbow. I guess it's from switching in different colored hands, but it only seems to be those particular colors.
In defense of China (hee, hee), I think the new minifig series aren't that bad. The difference is noticeable, but I haven't had any problems yet. Where some people have complained in other threads about the legs being too loose, I've found them particularly hard to pull apart. I actually gave up on pulling the legs off a leg assembly from one of the new ninjas and dug up an older pair of legs to use. I was impressed as I am a very strong individual. I guess smell doesn't loosen lego like the old story goes!