I use a Bluetooth keyboard and mouse under Windows 7 (64-bit) that started to hang from time to time after I began using Windows 7. I found that if I turned the BT radio off then back on it would work fine. Sometimes it would hang after I stopped using the keyboard or mouse for just a few seconds. Sometimes it was after I hadn't used it for several minutes. Regardless, I couldn't see any relationship to how long it hadn't been used and when it would hang.
I found if I went into Device Manager > Bluetooth Radios and opened the properties to ThinkPad Bluetooth 2.1 with Enhanced Data Rate and then unchecked the "Allow the computer to turn off this device to save power" option, the problem went away. [more]