Dear Miss Snark -- How long do editors typically take to get back to agents? Or (hidden meaning exposed!), when has it been long enough since I heard from my agent that asking her "what's up?" is a reasonable touching bases, not pestering?
It's not pestering to expect an agent to update you monthly. Some editors are quick, some projects are hot, but alas some of both are not. Thus, it's entirely possible that "nothing new to report" is the report. Even then it's reasonable to ask your agent where your project is and what activity if any has occurred in the preceding month. If you don't hear from her/him by the fifth of the month, it's ok to fire off an email asking "wazzup".