Woah! I am a little backed up with emails and questions after Miss Snark's awesome endorsement. I apologize if your question gets lost in the shuffle. Now, onto the questions.
What is a typical day for you? How many query letters or query emails do you receive? Do you read them all that day? How long does it take your boss to review the 5% you pass on? How long to respond with a final rejection or request for ms? Is yours a typical agency?
A typical day for me begins with me oversleeping and rushing to the subway without remembering to bring lunch. Then I buy some overpriced soda on the street because man, you do not want to lick envelopes without something to change the taste in your mouth. Then I forget the code to get into the office building and it takes a few tries for me to get it before I can get in.
I only come in once or twice a week. My boss, on average, recieves anywhere from 5 to 20 queries a day, which is fairly low but because she mainly does non-fiction and that generates less queries than fiction. Despite that, most of our queries are fiction or autobiographies. I usually handle the week's mail first, which has piled up in my absense. The mail is opened very carefully so that SASEs are not lost or mixed up with other ones. The maybes go in a pile for the boss, and the rest are rejected, put their envelopes, and sent off that day. (I believe strongly in not making people wait more than necessary)
Other jobs include some record-keeping in terms of tax-deductible office expenses. Occasionally I have to check a contract against a standard contract from that company and note any differences, as publishing companies are notorious for inserting or removing a crucial line to their boilerplate contract in hopes that the agent won't catch it. An average contract is a good ten to twenty pages of legalese, so this is an intensely annoying job, but it has to be done.
Very often my boss has me read partials or whole manuscripts, either because she wants me to look them over first in case they are so obviously bad that she doesn't need to bother with them or because she needs a second opinion. Occasionally I copyedit the manuscripts of new clients. She spends most of the day on the phone or at the computer (she does a lot of work by email because she has many international clients and does a lot of foreign rights), handling whatever's necessary to promote her client list. Often this means yelling at or comforting crazy clients who don't get their work in on the date they promised or are calling to complain that the champagne at their last book party was too warm. (I wish I was kidding, but if your books are pulling in half a million dollar advances, you get to do that kind of shit) She also goes on those infamous three-hour agent lunches with house editors, which don't involve eating slowly so much as talking about a manuscript nonstop.
Occasionally she has me sort paperwork or bundle books to be shipped out to foreign agents, but there's very little of that.
Her response time will vary hugely, depending on what author is having what crisis or what book fair is coming up. Rejections are usually faster than acceptances, especially if the partial is really bad. On a slow week she'll get to a lot of partials. When a client has hit the bestseller list, she'll be on the phone day and night telling everyone everywhere and arranging for him/her to be interviewed by radio shows and TV shows and partials will stack up. So it's really unpredictable.
My day ends whenever I finish whatever there is to do around the office. I don't have a computer and we share the same single-room office from a larger office space so it's fairly difficult to pretend I'm busy when there's no work to do. This may explain the low numbers in my checking and savings accounts.