I'm assuming you mean those black graphite sticks... i've never seen a straight up plastic drum stick before.

Pros: they're incredibly lightweight, they seem to absorb shock a bit better than wood sticks, they're about the straightest sticks you could find, and they last longer than wood sticks (mine actually lasted me a year and a half), I remember them producing a pretty defined sound too... especially on tom toms. Better weight distribution than aluminum drumsticks.

Cons: while the sound may be crisp, they didn't seem to produce as much volume as wood sticks do. Some of them have too slick a texture and may slip a little more. More expensive than wood sticks.

I had a pair of the Aquarian 5As, and as far as synthetic sticks go.... i thought they were great. I actually preferred them over the aluminum sticks.
I use 7A graphite sticks, the biggest advantage is that I've never been able to break one, whereas I go through wooden sticks like there's no tomorrow. They don't cost more than mid to high price wooden sticks, so they are cost effective.

I personally don't mind the sound, but they sound less 'organic' than using wooden sticks, which have more of a natural resonance. The graphite sticks make cymbals sound more harsh and less musical, wheres with wooden sticks cymbals to me sound a bit more harmonically rich and less brittle.