I recently purchased a Bluetake BT500 bluetooth mouse. And what a fantastic mouse it is. Anyway, I found that it does have some problems when using it with the Apple Wireless keyboard. If you connect the Bluetake BT500 mouse BEFORE the Apple Wireless keyboard, the mouse will keep losing connection every 15 seconds or so. If you connect the Apple Wireless keyboard BEFORE the Bluetake BT500 mouse, all will work perfectly.
And by connect I mean switching on the device after it has been successfully paired. It doesn't seem to matter what order you pair the devices in, just what order they are connected each time you turn the Mac on (or wake it from sleep).
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040527183650255