"And if you get bored and stop, that's because you're WEAK, damn you, weak!"
Fisking myself.
It also has to do with what boredom means in different contexts, which may be what you were trying to get at, Pete.
These are of course overlapping categories and gross generalizations, brought out for the purpose of making a point, for whatever it's worth -- possibly nothing at all.

Experimental writers (I call myself one) tend to emphasize intellectual engagement. If a piece is interesting to me for some intellectual reason -- for instance, Robert Sawyer's _Hominid_ series, or Samuel Johnson's _Rasselas: Prince of Abyssinia_ -- I can read past the craft issues. I sort of giggle at Sawyer's "I added a funny hat, voila, it's a character" issues, or his "and now watch me exposit through dialogue! Surely you won't notice, Bob!" -- and meanwhile, I read those three books in like three days, and then wrote him a fan letter, because I loved the anthropology so much.
Literary writers, esp. the ones in the midst of an MFA program, tend to get off on craft execution a LOT. A story that surprises us -- fuck yeah. That's like teh awesomest thing ever. We tend not to be reading immersively (because we're in the middle of overanalyzing everything to death -- and yes, I'm spoofing us a bit here) and so we're watching the story's bones. So, the kinds of things that are enjoyable qua enjoyable are probably going to make us roll our eyes, because we are overexposed to narrative trickery and can spot a trick whe we see one. On the other hand, a tedious but well-executed passage is appealing on the bones-level.
Literary readers... eh, I'm over-immersed in MFA culture, so skip that one.
Genre readers, on the other hand, will often talk about boredom and enjoyment in the way that, well, our culture uses the terms. It's enjoyable because it's immersive and exciting and fast-paced and fun. It's boring because one isn't interested in what the text is doing, and I have usually found most genre-readers and -writers to use this in the sense of what the text is doing as a text, not what the text is doing on a meta-interpretational level.
It's that last point, I think, that I was trying to make. If it's clear at all. And if I haven't wandered.