ECO = Entry Clearance Officer. The people who will open your application and decide where to go from there. Not enough documents, declined, no questions asked, until next year 2013 people can dispute a rejection, but after that they are gone, rejection is final. They might pass it on to another ECO who deals a bit more with something he is slightly concerned about, or he might make a decision and authorize entry as it's a clear case with no issues. The more ECO that have to look at the application the less likely they are to accept it, hence a quick response is usually good news, delay is usually bad.
Really, they've made it so so difficult now, a bit like being guilty until proven innocent.
They don't employ rocket scientists for this job either, you can get some ****ed off idiot who feels like being nasty and just declines randomly, it is a crap system in the UK, and getting worse.