Background Vocal Technique

Lining up vocals is a tricky business. It's a lot like pitch-correction, in that a little goes a long way and over-doing it can actually ruin an otherwise good part.
 
I don't have Platinum, but I've used AudioSnap, V-Vocal and Melodyne for vocal alignment. In my early attempts it took me awhile to figure out why my BGVs were often getting worse after alignment instead of better. Turned out they were actually too closely synchronized, to the point where I was getting comb filtering!
 
Nowadays, I approach it much less vigorously. Some lessons learned:
 
1. Evaluate vocals phrase-by-phrase. Listen to each section in the context of the mix and ask yourself if it really needs adjustment. Don't assume that alignment is always needed and don't assume that it will always help.
 
2. Looseness actually helps extended vowels by enhancing the chorusing effect. For the most part, I only align consonants and short vowels and don't worry too much about anything else.
 
3. Instead of aligning consonants, suppress them. When you have multi-part harmonies or double-tracked vocals, only one of the tracks needs to supply the consonants. The others can be aggressively compressed with a fast attack. A multi-band compressor or dynamic equalizer works well for this. Taking a little off the top of the spectrum helps, too, in the 3-4Khz range.
 
Listen to old recordings that have lots of vocal layers but no digital timing adjustments. Jethro Tull and Genesis double-tracked lead vocals, Fleetwood Mac layered and doubled harmonies. Anything John Lennon ever sang. They're all loose, and they all sound f*cking great.