As readers we have to come to terms with the fact that we will miss out on many good books, there just isn't enough time to read them all in a lifetime. I decided stop reading the ones that aren't that interesting to me after reading (roughly) 30%-40%[1] of the book. If after this it hasn't grabbed my interest then it just isn't my kind of book, at least in my experience. Will I miss out on the rare book that gets its act together after the 60% mark? Sure, but in my experience those are very rare and I'd rather miss out on them than spend the remaining time chasing the elusive "it gets really good after the 60% mark" books.
> I've yet to be disappointed, even when the topics are somewhat outside my everyday interests and hobbies...
My experience has been the opposite of this. I have found a lot of duds in those lists (I'm talking about fiction books specifically)...
[1] All percentages are approximations.