POD-dy Mouth sheds a bit more insight into the agent rejection thing — specifically why an agent would love your novel but still decide he/she wouldn’t be able to sell it:

What you, aspiring writer, are forgetting, is that while an agent may sell (as an example) mysteries and yours is a stellar one, he/she may know that his/her editorial contacts will not go for your particular mystery for some offhand reason. Agents, to varying degrees, sell to the same editors over and over. Examples: Jenny Bent (Trident) sells regularly to Denise Roy (S&S), Dorian Karchmar (William Morris) sells regularly to Claire Wachtel (William Morrow), Elaine Koster sells regularly to Carrie Feron (William Morrow), and so forth. The point is these agents know what these editors want . . . specifically. So if your novel’s protagonist happens to be a coke addict and Agent A’s contacts aren’t much for characters with substance abuse issues, you’re out of luck, no matter how deftly written your novel may be.

Interesting. So to some degree, agents act as scouts for particular editors . . . you learn something new every day.