I have tried it once, it did not seem to move the bees down into the frames as quickly as real smoke. But it is a lot less hassle than lighting a smoker and relighting it once it has gone out before you have finished your inspection of your hives.
I have used liquid smoke on 7 hives for a few weeks now. Six of the hives need minimal smoke or no smoke as the bees are really kind bees. The seventh hive is populated with the nastiest bunch you will ever meet and are a challenge. On this hive I usually use some smoke, I have switched to liquid smoke and it seems to irritate them. I'm still using it but deep down I think it doesn't work. But as I don't end up smelling like a kipper I am persevering with liquid smoke.