As some of you might have noticed already, I tend to digress quite a lot. I don’t really see the problem, though - most matters, especially the ones discussed here, are too complex to understand fully if you don’t put them in context. Also, at least to me, it doesn’t matter too much exactly what is discussed, but that something is, and digressions have a potential to keep a debate alive (unless people shun them). If something is important, it will be returned to anyway.
What do you feel?
My cat’s breath smells like cat food.
If everyone stayed on topic all the time, the SDMB would not be what it is. The occasional inside joke or Monty Python quote or amusing anecdote is what makes people want to ask a question in GQ, rather than wading through pages of results on Google or Wikipedia. As long as your point is at least tangentially related to the OP, and doesn’t cause the thread to derail entirely (which does happen sometimes) I see no problem.
Exactly–what I like about this place is that it’s like an old-fashioned salon (and sometimes like an old-fashioned saloon). It encourages conversation, and the best conversation oftimes involves digression, drive-bys, wisecracks, and “oh, that reminds me of something that Wordsworth said to Sophie Tucker.”
Other than government reports, academic journal articles, and other highly formal stuff, there isn’t any place where people should stay militantly on topic. Discussion should imitate real life, and real life doesn’t stay on topic either.
It only gets irritating when people automatically make the same diversion over and over again, because then it becomes as regular and formal as a discussion with no diversions. So the people who link to Onion articles in every single Great Debates thread or bring up the babblefish in every single religious topic are the ones who I can’t stand, just as you eventually want to punch that idiot who quotes Monty Python every single time he speaks.
How do you feel about Simpsons quoters?
Anyway, any attempt by an OP to keep a subject narrowly focused on his/her particular interpretation, I have observed, is routinely met with derision. And don’t ever say “This is MY thread”. That’s an express ticket to train-wreck city.
Tangents are generally welcome, or at least tolerated. Some people get steamed, though, if you derail a thread before there has been an attempt at an answer. As Brian Ekers could tell you, some threads just cry out to be blindsided, even in post 2. 
It’s like a jam band. Sometimes a solo riff increases the Cosmic Groove Quotient.