When I was 5, DGF took the family to
Disneyland. My mother carefully explained to me that we would go on absolutely everything I wanted, but we'd have to wait on line and be patient. So I was and we did, including the Matterhorn (my most memorable ride from then). Obviously I have no memory of how long the waits were back then, but the principle that patience is rewarded was burned into me.
Nowadays, like many have said, it really depends on the ride and circumstances. I remember doing long waits from outside through a full queue at SpaceMtn. I also remember one very long wait for Splash, probably 90 minutes. Both of these were pre-FP.
I've been on the overwhelming majority of rides at WDW, and would probably limit myself to 15-20 minutes for the very familiar ones (like GMR or Small World). Even then, if we had nothing better to do, I might go longer - we almost never ride the same ride twice in a day. For some familiar repeats that are exceptional, such as SplashM, I'd start out with longer limits (especially in the Sep. heat).
Among the rides I haven't ridden, I'd be willing to do an hour, maybe more for EE or Mission:Space, and possibly PP to see the new queue. From everything else I've read, 7DMT is overhyped and simply isn't worth a long wait. I'd also give Dinosaur extra time, as I've only been on it once. TSMM sounds too much like Buzz Lightyear (I welcome corrections if that's wrong) to justify a huge wait. I don't think there's anything else at WDW that would justify a huge wait for me.
On the other hand, I'm willing to wait as long as it takes for the Harry Potter rides, and probably some of the others at USO. There's just more innovation there these days. I remember putting up with long waits for Doctor Doom and Spiderman there, worth it for Spiderman, less so for Doom.