I generally tend to always read smaller posts, and if it's an issue I feel strongly about I bump that up to all posts. I do agree with some others though: If I lose track of a debate in EoEo or something, I try and "resume" reading from the last few posts.

In terms of members, it does depend. If it's a thread I have started, I will definitely scrutinise each post, no matter who. In all other threads, if it's a friend, or someone I care deeply for, I will definitely read any and everything they have to say.