What version do you run (firmware)?

Also, I got that too when connecting through a hub. Some hubs do that, and remember, the ports in the PC are in a hub as well, using an external hub is cascading already.

I have this really convenient vertical port hub I like but every now and then just spits out my N900, my Sony Alpha and a few other devices. I have to reset the whole chain (all cables unplugged, all hubs powered down, etc).

Might be a localized issue. Try back ports. Try non-hubbed. Try a friend's USB. You might well have a compromised USB hub. It's way more widespread than people think.