I rather like performing games like SingStar or Performous, but what they can teach you is in general rather limited. Most of your technique will be based on practice, and with things like Rock Band, that’s not going to be much good because the instruments aren’t really playable (though Band Hero’s drum set comes closer, being a MIDI set). In addition, they tend to use a simplification of the standard notation.

Recently I came across an exception. Piano Booster plays common MIDI files and expects you to play along with a MIDI instrument; I’d encountered keyboard specific ones before, but this time is uses standard notation. In addition, the difficulty is much more tunable than I’ve seen elsewhere – you can choose what track to play, adjust tempo and transpose, restrict hands (for piano) and even get it to pause the music until you get the chords right. In short, it’s more of a trainer than a game, and a competent one at that. For more details, check their website.

(Found, like many of the things I hear about, via Debian.)