I also have experienced this and it is a pity, because TR is an extremely useful app but those speed issues are slowing down the process of organizing your ideas about things to get done.
From my experience, navigating in the "review actions" and "review projets" panes is quite slow and entering data in the text fields in projects or actions can become a pain.
(I used a PC with Windows XP SP2 and the hardware is powerful enough to do 3D CAD and other things without too big problems.)
I hope that this lack of speed in the GUI can be overcome at the end of the test phase of TR2 because more "responsiveness" of the GUI would be highly appreciated.
p.S. Don't get me wrong! I LOVE Thinking Rock and it helped and helps me changing my life to a more organized one because it was with this software that I finally (after several attempts) really understood the GTD workflow and was able to nearly "implement" it in my life.
However, a software that feels like a block of concrete tightened to your feet feels counterproductive for getting things done as quick as possible.