Virtually every bitcoin user already uses third parties, and trusts them to some extent.  Doing so is a trade, cost for risk.  In the future, I expect it to be even more complicated.  Imagine a credit card denominated in bitcoin.  With that, you'd be paying for them to assume transaction risk for you, while right now the model is mostly the opposite with you getting a discount for assuming the risk that the third party may bail with your bitcoins.

Every bitcoin transaction has a cost associated with it, and we don't have a very good idea at all what that cost really is.  The mad scientist in me thinks that we should wait until the 1 MB limit is met and sustained for a while before we raise it.  That way we'd get some real world experience with how the system (including the people!) react.  Hopefully, that would lead to a better understanding of the forces that will eventually drive the equilibrium.