The little pools of water from blood/goo aren't the issue, it's running water that accumulates over time. So I think it's multi-threaded, even if it's still too slow for fluids, and it is FAR better optimized than say Arkham Asylum which is unplayable without an Nvidia card if you want PhysX (and quite clearly uses only one core if you check). I run with PhysX enabled (ie med or high, low is basically 'off'), I get moderate use of all 6 cores with it off, BL2 mostly uses just two cores.
