The most recent release of Cakewalk Sonar includes a plugin called "R-Mix." In short, it's a visual audio manipulation tool. It's like looking at sound as it's coming at you (as opposed to it scrolling by you from left to right). It's great fun to roam a recording, choosing where in the stereo field to listen. It's like using a shotgun mike with an equalizer.
In the past I may have said that I learned to work with MIDI by taking songs apart and making backtracks. My brother was singing to backtracks at the time, but they were vocal removed tracks (using the LT Sound Vocal Remover that many of you may have seen heavily advertised in magazines "of the day"). Since vocal removal didn't work well on lots of records, there was still a need to record our own backtracks. The reason these records didn't "vocally remove" was the vocal remover would cut out any center track voices or instruments in the vocal range (usually the drums and bass). It had a low pass filter that would allow low frequencies on the center track to pass through, so you would get at least some bass and bass drum. And it wouldn't delete any reverb/echo outside of the center track.
It worked great on songs with only the lead singer in the center track with no effects. I remember the original "Layla" was one it worked perfectly on.
That said, R-Mix is vocal removal on steroids. You can create a rectangle or oval, size it and place it over the lead vocal, and adjust for maximum volume. Then you can reduce the volume of the selected area and bring up the volume of everything else. The result is vocal removal. You'll still have effects that may be outside your selection, but you can find a plugin for /reducing/removing reverb nowadays, too.
And speaking of backtrack recording, the hardest part of getting a backtrack right is hearing all the parts. With R-Mix it is MUCH easier. On many modern recordings, you can find a particular instrument and isolate it in the mix. I took some recordings I've done backtracks to in the past and heard things with R-Mix that I never heard listening to the whole mix. Such things as what effect is being used on an instrument, when the instrument is playing (in a muddy mix) and what the instrument is playing.
You can learnsome secrets of good mixing by slicing recordings up with R-Mix.