JJ
I've tried it a few times and I noticed that it did help to clear the beer faster than it would have naturally.
I consider it a big advantage when I'm in a hurry - since it clears the tannins relatively fast. For example if I have brewed a light beer and want to serve it at a party in a month I will drop some polyclar in a few days before bottling to expedite the ageing process.
I consider it superior to gelatin. Yes, it is plastic, but it sediments out with the yeast and tannins, so I've never noticed any ill effects.
Don't boil it! (it will melt) - I just add it to some distilled or pre-boiled (and cooled) water and then gently mix it into the secondary.
Cheers!
Brad