Well returned the v270 and tried a MS 8000 (vista certified) same problem. Even when the blue tooth software shows the mouse status as connected the mouse software sees it as disconnected/standby.  The only solution to get the wheel to work is to turn the dell radio on and off. This is why the mice will work when coming out of sleep because the computer turns the radio off going to sleep and back on when it awakes.  You have 1 of 2 choices do not buy the dell BT solution w/ vista because most probably any brand mouse is not going to function correctly as I've tried 2 w/ the same problem.  The 2nd choice is to set you hotkey Fn F2 to turn on and off the BT radio when your scroll wheel quits working.  This is easier than going to the device manager and turning on and off the radio or taking you computer in and out of sleep.  Maybe dell and/or MS will fix this communication error between drivers sometime in the future?????