Hey im getting the exact same problems too. I play starcraft a lot and this has really deterred me from playing it on my comp. Mine is evident by the slow movement of the mouse. Normally when u experience lag, your mouse pointer goes at the normals speeds. However, everytime i play the mouse is slow and jumps to catch up to where its supposed to be (kinda like a strobe light feeling).
SpeedZealot: Look at the screens when it goes from the "connect to which server" page to the sign in and Bnet screens. They should come up instantly with no signs of transitions. (Mine, however, takes about 2 seconds to go from screen to screen.)
Facebook
Twitter