+1 I love the idea OP, but it should probably not be a mandatory function of the Satoshi client. Better as an option built into many clients.
The reason it shouldn't be a mandatory part of the Satoshi client is that that client should strive to avoid feature-creep. There is value in simplicity, especially for the core client. But if this option became standard in the Advanced tab of all clients, I'd be a happy man

My take is that it should be
part of the Satoshi client, but turned
off by default. I think that's what you are suggesting, right?
I would agree it should be off by default for several other reasons including: it leaks information to the public that some might consider private (such as the fact that their node and wallet is online and alive), and it also results in confirmed funds suddenly becoming unconfirmed and then reconfirmed at random intervals (though not at a risk of loss to the wallet holder).
None of these things should occur to users who don't understand them or explicitly opt in to them. They could be briefly explained as benign side effects to a user who checks a checkbox to enhance his anonymity.