I like going in to new stuff blind, but that is only stuff that is really and truly new. Figuring out boss mechanics is fun, but if it's likely that most of my group already knows the fight I'm going to go ahead and read up on it in advance because I'm not going to figure things out regardless. It's just going to be explained to me, and I'd rather use the limited time in the instance to work on execution, not get a hgihly abbreviated explanation of what I'm expected to do when.
I generally hate being the weakest link in a party, and while there are certain things I can't overcome (lol no skillz), I can largely take responsibility for making sure I'm informed on a fight and understand what's going on with all the pieces at any given time.
I don't get angry at new people on DF who haven't read up, unless they immediately demand somebody explain the fight to them. You want to go in to T5 blind, that's fine--We're not going to clear, because the time to learn that fight from complete scratch is usually greater than a single instance timer allows--but I don't actually expect DF groups to clear it. But if you're going to zone in with a group of total randoms and then immediately expect somebody else in the party to give you cliff's notes, there's no spontaneity there and it comes off kinda lazy.
All bets are off for FC parties, though. Come as blind as you want, I don't care, I'm already planning to repair constantly. But FC parties aren't generally restricted to a single lockout before the party scatters to the winds and has to start over.