I noticed today that while smoke grenades distract zombies, it only works for a little while. I aggro'd a horde while looting, they were right on me and I wasn't near a building so I ran to get out of town (alerting more ofc), once out of town I tossed a smoke right in front of me and ran over it. All the zombies stopped and circled it while I ran off to bandage. I didn't trust it so I rested about 100m from the pack, watching. Sure enough, when the smoke stopped they started at me again. Luckily with 100m separation and my M16 they weren't a problem, but it's worth noting that the Z's will default to thier previous aggro after the smoke wears off.