Do you read the whole thread before you post?

[Shiloh Lundahl]

I find that I get annoyed sometimes when I am reading through a thread that has several posts (let’s say over a page worth) and someone new chimes in and either asks a question that has already been answered or writes something like “I’m not sure if anyone else has brought this up yet, but...” when it has already been brought up and discussed thoroughly. 

When you comment on a longer thread, do you read the thread through all the way before you post, or do you just post your comment without reading through the whole thread first? Why or why not?