At what number of terrible Bluetooth software stacks does one start wondering if there isn't something fundamentally wrong with the specification that makes it so incredibly hard to get right?

It's been bad from day one with Widcomm and later Bluesoleil on Windows. Mac OS X for years had a Bluetooth where after a couple of hours of using the DUN profile it would need a reboot, on an otherwise nicely reliable operating system. Mice on Bluetooth have never worked as smoothly, reliably, or as well as just using a proprietary protocol like Logitech Unifying.

It's not that I necessarily think it's an unsolvable problem, it's just that after a decade with so many multiple implementations that can't get it right I feel Bluetooth itself has to bear some responsibility.