General Spelling and Grammar: Mostly, I just need to understand. I don't really care otherwise.
Pose Length and Detail: What I need is for every pose to have give me something, I don't care how much detail or the length of it is. That said, people who pose very small are likely not giving me a lot to respond to: but I've known some people who were gems at it. So, too, I've seen people who write novellas per pose and have absolutely nothing I can do with it. Multiple long paragraphs with maybe two words, and none of those paragraphs really usable content. Its downright frustrating.
Tempo: It depends. For me the point at where I start wondering if someone fell asleep is the 15-20 minute mark, but as long as I know its a slow scene, I don't mind. I usually try to get my pose done in five minutes after the last person posed, but this is because I start writing my response while other people are posing, and just adjust as each pose comes in, sometimes completely rewriting it. But this is why I prefer round robin in any scene <= 5 people: at this point the chances of someone invalidating my pose complete is high, and I get into this trap of never finishing. For bigger scenes, I see 3pr as a needed evil because otherwise I find it impossible to keep up... but even then, I will tend to do that for maybe an hour then just blank out and mentally check out of the scene because its too big to keep up with.
Personal Peeves: You-posing is completely creepy: I do not identify myself with my character. I don't mind metaposing as long as it is treated as something that can be read-- body language, tone, intuition-- or if its directed entirely at oneself. I do not want to see 'Jane smiles warmly to Bob, even though she thinks he's a jackass for showing up'. You don't get to call Bob a jackass and not take the heat for it. Now, if she posed, 'Jane attempts to smile warmly to Bob, though her irritation at him over just showing up makes it difficult', that's fine. Bob can still respond to her 'tone' or attitude or something, its not just essentially OOC commentary mixed in an IC pose.
What annoys me is when people don't take the OOC agency to involve their characters. This is my biggest pet peeve in the world. If you are playing shy, that's fine. Its still YOUR JOB to come up with a reason to get your character to engage with others. I've played shy characters before: I don't have them sit in a corner reading, waiting for someone to drag them out-- I make up a scenario that gets them out of their shell for some reason. (Maybe they're a clutz, and oops! Bumped into you. Damnit now we must make social noises).