leaving your client running 24/7 is an invitation to a hack. you know -- port scanners?
If the client has a vulnerability that allows someone to steal from it over the network, I'm willing to lose a few coins in exchange for knowing that. The network needs high connectivity stable nodes that can accept inbound connections, and I'm more than happy to provide a few. (The total number of bitcoins stored on all the clients I keep running continously -- less than 2.)