Most of the larger TGP's open in the same window... but...
if you are running a small to medium sized (under 100k) tgp and rely on trades and click productivity I would recommend new windows for the reasons Amp mentioned. Especially if most of the sites you are trading with pop galls in new windows cuz the surfers are trained to close that window and if it was the one your site was in then that's the only click you'll get out of them.
