Recently I had the chance to participate in an eye opening exercise. I became an agent for a day. Not for real, just on a blog, but it really proved how hard an agents job must be.
I recommend you read this agent's blog http://www.nathanbransford.blogspot.com/. He posted a contest where he listed 50 query letters and asked for our opinions. What would we say if we were an agent? How would we reject manuscripts? Would we use form rejections? Would we be able to move quickly through all the query's? And as an added catch, we were only allowed to request 5 manuscripts out of the 50.
I was amazed at how time consuming it was just scanning letters. I definitely fell into a pattern of form rejections just to save time. I also discovered how easy it was to tell the good query from the bad. It was very obvious from the first paragraph whether this would be a manuscript I'd be interested in. There was rarely a need to read the added manuscript pages. Of course real agents must have a wide list, a list that will sell, and I only focused on what I personally liked.
After I read through about 30 queries and left responses my eyes were already tired and I wanted to move on to something different. An agent must go bonkers. Reading and responding to queries in only a small part of their job, yet probably the most time consuming one. Nathan Bransford mentioned he reads around 75 a day!
So, now I know not to feel so bad when that rejection comes. And believe me they come. It really is a very subjective thing. Whether you need to have an agent or not- that's another post.