Ok, I'm stuck in a coffee shop using public wifi. I'm pretty sure some jerk is torrenting and ruining the connection for all of us. Astoundingly, the place using a wrt54g with a default router config. password. If I knew who it was I could handily kick them off, but I have no way of telling with out using a bandwidth monitor. Anyway, that gave me an idea; is there some kind of passive network bandwidth monitoring software for a client? Specifically, something that gives up/down bandwidth stats for the each client on the client table. I'm about to head out so I'm not going to fuss with it now, but it sounds like a really useful thing to have.

this is bad and you should feel bad

There's nothing bad about wanting some douche to stop leeching all the bandwidth.

This sounds like some quality creepin'. I approve.

WireShark?

Etherape or Lanmap\

Edit: I know this because I've spent a lot of time procrastinating in coffee shops and end up more interested in who else is on the network than doing anything productive with it. :p

I would suggest telling the owner of the coffee shop, but since you have said they are using default configuration including password, I will assume that the owners probably will have no idea how to rectify the problem.