Our team just finished doing usability research on Visual Studio's setup. These studies are always fascinating to me, because even the most seemingly simple interface can completely crash and burn when presented to someone who is not biased by the effort that went into designing it. One of the things I see repeatedly is how little we actually read UI that's presented to us. When it comes right down to it, the human mind is amazing at skimming text.
Anyways, just about every time I watch users install software and get them talking, they gripe about the progress bar. For Visual Studio in particular, we are notorious for taking a long time to install (hey we're working on it; there's just a ton of stuff to install!). In some versions, the progress bar is accompanied by a text message estimating how long it will take to complete the install. This estimate is kind of like a asymptotic, sinusoidal graph. It goes up and down wildly, and--cross your fingers--gets closer to its target as time goes on. I think we have all been taught overtime to be skeptical by the application that gets to 98% done and then stops dead in its tracks. Do people even trust progress bars anymore? It seems like more than anything I use them as purely an indication that xyz program just hasn't crashed yet. Maybe I just have really low expectations.