Finally had a chance to go through a few things on my Toshiba 56MX195 - As far as I can tell, no lag on anything. In case anyone is looking into a Toshiba I thought I would post my thoughts. I avoided the Samsungs entirely while shopping due to this and similar threads, discarded the Sony due to price (loved it in the shop though) and took my 360 in for a showdown between this, the JVC 1080p models, and a few Mitsis.
For what it is worth, in the store I didn't notice any lag with the 360 (component in) any any of the 3 models I looked at. The Toshiba got purchased due to it's brighter picture, smoother display (compared imho to the mits) and a slight price advantage. The mits was too dark, but the JVC vs. Toshiba was a tough decision.
I have run a PS2 via component through a pelican switch box and tried DDR Extreme and Guitar Hero and did not notice any significant lag at all. It may be there, but it is miniscule at best. I actually pulled a better score on a few songs (on medium difficulty, and without having played in several months).
For the 360 I have run it through component into the pelican, component direct into the TV, and VGA direct into the TV. Played Geometry Wars, DOA 4, CoD2, and Burnout Revenge. GW and DOA4 are the 2 I would suspect lag on, and apart from just looking stunning, I didn't notice any serious issues.
If anyone has any advice on how to measure something like this let me know and I will see if I can detect any lag, but so far I am happy.