I have a bunch of created sim couples, mostly to save time and prevent the need to compete for love interests vs MCCC matchmaking exactly a day later at 2AM game time. I'd be lucky to find any sim left behind and before the 3rd day as at that point it becomes a race between marriage to new random sims or being alone and pregnant. At that point i have no interest in that female sim. The only male sims left are the usual types that prefer to be on their own.
I'd like to have a far more interactive and more organic way to build friendships and relationships, i don't see it on TS4, but then again half the material needed to make it organic would never be included.