I posted my winamp playlist in another thread around here. There's about 2000 songs on it, and you can check for yourself how much of that is copyrighted. I am willing to bet that there's less than 300 songs on there that the original artists would want to protect, and there's even less on there that's actually popular. Most of it is composed of game soundtracks, OC Remixes, or movie soundtracks, or simply my own CD rips. Regardless of amount, I do recognize that it's stealing. I don't think that it's any worse than lifting a chocolate bar from a corner store though.
For emulation of old systems, such as the NES, SNES, Genesis, etc, I have to agree with Shifty. I am undecided whether it's right or wrong. Regardless, I do it myself, and when I do, I am reminded of a quote from Shigeru Miyamoto. When asked what he thought of emulation, he responded by saying that he was happy that people still enjoyed playing his games.
For emulation of new systems, such as the PSX, N64, or GBA, you have to accept that it's outright theft. It's not theft of a devalued object such as an '80s NES game, or something as trivial as a single song that's played repeatedly for free on the radio. You are stealing $60 worth of popular software, that the developers worked hard to make.