Well, expense is definately a drawback.
If you reload it's more expensive to reload than 9mm, but a tick less than .40 to load because it uses standard 9mm bullets.
357SIG, in a good gun, tends to be more inherantly accurate than .40 (No idea why.) and is ever so slightly more accurate than 9mm.
Another drawback for the 357SIG is it's optimized for 124-125 grain bullets. Sure, others are available, but 9mm+p+ 147 grain bullets can basically do what the 357SIG can do with heavy bullets.
One nice thing, though.
It feels like a small 10mm or 357mag when you shoot it.