In general, I think this is pretty true of web apps and business applications, but when its things that will generally push a system to its limits performance wise (in particular, games, 3D rendering, Compositing, etc), people do tend to notice. For example pretty much anyone who regularly plays Team Fortress 2 can quite easily tell that its an incredibly badly optimised game (written an already badly optimised engine), simply due to the fact that if they load up Call of Duty 4/5/6/7 with the same graphics settings, they will get literally twice the frame rate, or even Left 4 Dead which is the same engine.
Also my point with compositing, the built in lens blur effects in Adobe After Effects take exponentially longer to render than a number of better third party plugins.