i leave 4 separate clients open and i don't even mine. i do it for philosophical reasons to "help" the network. doesn't cost me anything.
Everything costs something!
If bitcoin becomes fully fledged monetary system things like enthusiasm, altruism, philanthropy and philosophy will not be enough to secure its future! After all, it is about money! All tricks will be used both technically and economically to game the system and abuse it. Every expense that is possible to avoid paying will not be paid by participating agents in the network! There is no doubt about that... The big question here is whether all those avoidable expenses are fundamental incentives to keep bicoin network running?
I don't think of the Bitcoin client as simply a way to spend Bitcoin, even though that's about all it is at the moment. I think of my computers as machines for (sometimes monkey) business. If you want a productive business, you find ways to keep your machinery running 24/7. I think that will be the goal of software designers to craft tools using Bitcoin to stay on making money. I'm not talking about mining, but real world businesses that will depend on a robust Bitcoin network.
I wouldn't be surprised if M$, Google, Facebook, Mozilla,
, (pardon my bias) etc. doesn't have NDAs regarding major development for BTC based apps. I can't imagine big ballers not creating Open Transaction servers, microtransactions, anti-spam postage based email, deed of title apps, escrow based courier services, and probably hundreds of other unique products and services that take advantage of Bitcoin's unique properties.