I had erratic touch screen response on all my android devices (Galaxy Tab, Nexus One, G2x, Sensation, Transformer) when using cheap USB out adapters. I never have a problem when charging from my laptop. I typically don't have any problems when using the OEM chargers, but I haven't unwrapped/used the one that cam with my Sensation yet, as I have plenty of other to use.
My guess is there is some AC leakage on the ground pins of the charger, which interferes with the capacitive touch screen. I suppose I could hook up my oscilloscope tomorrow to see if that is the case. Regardless, my solution has always been to use a different charger.
T879 Note on T-Mobile
Do not quote my entire first post in a reply!