Tony and Lee..pitch correction does work in real time..I would say the higher quality units will work better..

Vocoder mode is the easiest way to achieve what you are after..

It would depend how accurate you play the keys [on key]...and the timing of your voice to what you play[although it is easier to play to your own singing]..

You can also rely on lead tracks if you are using SMF's...This also depends on accurate timing of your vocals...

Unlike other folks comments ..I think it can improve your vocals...and also train you to sing on key...

Matter of fact a harmonizer can make a great singer terrible just as easily as a poor singer....Misuse of a harmonizer can kill a great vocalist too..