If your client has the wrong idea about what they want, what you're delivering, or what is possible, then you're failing to do your job. There, I've said it. Their job isn't to know the technology; that's why they hired you. If they do know a bit, then it generally helps, and I'm a firm believer that if a client commissions work then they should try to understand it (at least on some level). The point is, though, that they have other things to do that don't involve knowing every line of code, the limitations of various browsers, or how much data you can (and should) push through a pipe.