Weezing GE is one of those "fun" cards imo; they might be fun to pull off at League or something, but they aren't viable enough in the prevailent metagame to win against the major decks out there. Anyways, Weezing has the usual Stage 1 stats (80 HP, +20 Weakness to Psychic, but a slightly costly Retreat of 2). Toxic Virus is a great Poke-Body, giving basic Poison status what I call the "toxic" effect (2 damage counters inbetween turns instead of 1, more if the attack effect states otherwise), making it possible to do a solid 40 damage inbetween the turns to your next turn. Offensive Gas is moderately priced at 1 Psychic, 1 Colorless Energy to use, doing 30 and a chance to Confuse and Poison with the flip of Heads.
Along with Weezing, I'd like to touch up briefly on support Pokemon for it. There are a wide variety of Pokemon that discourage Retreating to get rid of Poison or offer some faster way of doing Poison. These include Skarmory EX, Ariados, Toxicroak, and more. More information can be found in this thread:
http://pokegym.net/forums/showthread.php?t=66775
Modified - 7/10 (Can be used in a fun deck, unlikely to win more beyond that sadly)
Limited - 9/10 (Decent cheap card, Poison adds a lot more here, making crucial KOs possible)
Unlimited - 1/10 (No use here, you're not going to force someone into a Poion-lock here)