I think they're okay and after trying a few they've seemed nice to ride, but nothing truly worth buying a new bike over in my eyes. Compared to a chain SS / IGH bike, chain guards work fine and also keep your pants, laces from being sucked in, a belt drive will still need a guard if you want to prevent things from being caught in it. 1/8" chains last forever, install easily, and can be bought for $10 nickel plated or $20 stainless steel. Sprockets and chainrings are really easy to find and change, belt drive cogs are currently not.

I use a stainless steel chain. With the chain guard, it needs to be lubed maybe every few months, it lasts a few years, and it doesn't cause any grief with my clothing. Maybe someday it will be worth changing it over for a belt drive, but i'm quite happy with my bicycles as they are now, and don't want to give up a whole bike just to have a cute new belt drive. Given that to me the gains seem overblown, it isn't worth it to toss away my bikes for this stuff yet at all.

Maybe if there was a bicycle I really liked that had the belt, sure. But i'd still shop around for all types of bikes, and would put belt as a "nice to have", and not something to base the whole search on, personally.