The regionFX VocalSync works fine, but sometimes I have to resort to the Hard Way, and am posting to see if someone is going to tell me there is a much easier way than this (although it does seem to work fine).
 
Suppose you have 2 tracks, Vocal and Harmony (or whatever).  Timing on Vocal is fine, but Harmony doesn't exactly line up with every phrase of Vocal, and you want to match the starting point of the phrase "baby" in Harmony to match "baby" in Vocal.  Here's how:
 
Set Options, Drag and Drop, to Blend; set Autofade to ON.
 
1.  Split the Harmony track before AND after the word "baby".
2. Show take lanes.
3.  Drag cutout to empty take lane.
4.  Slide "baby" forward or backward to match.

When Vocal Sync doesn't quite cut it, I go back to using Audio Snap. Drag each transient by hand to match up with the other vocal. Audio Snap is enabled on both so that you can see the transients.

GregGraves
 
1.  Split the Harmony track before AND after the word "baby".
2. Show take lanes.
3.  Drag cutout to empty take lane.
4.  Slide "baby" forward or backward to match.

 
I do this except I don't use a different take lane. So far I haven't had much luck with Vocal sync though.