I generally use limiters on vocals, clean guitars, and the bass guitar...really anything that has a lot of quick dynamics and needs some serious taming to sit in a mix, but it's generally a small amount, in conjunction with other stages of compression. A lot of times with clean guitars it's very effective to shave off just the top few decibels of a signal with the limiter first, to lessen the impact of a compressor that's next in line (especially when you want a quicker attack). The same general principle is generally true on any source, though...that is, when there's a lot of dynamic taming to be done, spread it out over a few different tools instead of slamming only one. You can sometimes slam a limiter if you want to achieve a certain kind of coloration, but otherwise it's a tool to use in moderation. I generally never put a limiter on the master bus, except temporarily in order to mix through it. Actually, I recently rediscovered how much I like the sound of the Finalizer (which has a limiting stage), and it's really helpful mixing into it, basically for getting a mix to endure it and stay punchy.