I had an issue with my Skyrocket and SD Cards a month or so back. The phone would take 4-5 seconds to wake up when I pressed the power key. I had a class 4 16GB Wintec MicroSD in there. When I took the MicroSD out, the phone jumped right back to normal.
Has anyone else had this problem, and more importantly, has anyone else using a Class 6+ MicroSD noticed lag time between waking the device and the display coming on? I might have to go get myself a Class 6 (if not Class 10) MicroSD if everyone's had good luck thus far.