Summary: Warning to Mac users. I'm an IT guy at an entirely Mac organization. We've found that if more than one Mac nearby running 10.9 is paired to a HP x4000b, it tends to cause the Macs to freeze at sleep or screensaver. We've been able to reproduce this behavior consistently. Other bluetooth mice don't have this problem. However, in situations where there is only one Mac and only one x4000b nearby, we've found the mouse performs as expected.