I joined just to toss my hat on this. I must have groups working as
well. While everyone here is mentioned Google Voice as the catalyst
(which makes sense), my catalyst is OS X itself. Since everything ties
into the Address Book, I have tons of groups for specific purposes,
such as Billings (for the software app Billings), Screen Names for use
in iChat, Reunion Peeps which is a listing of classmates for my
upcoming reunion. All of these groups need to be on my Macs for OS X
purposes, but only a select few are synced to my iPhone. The ability
to keep this grouping is very very important to me, and is pretty much
the sole reason I keep my MobileMe subscription (even though Apple
completely missed the boat on OTA syncing since it also doesn't allow
selective groups to sync, its all or nothing).