This has happened to me a number of times (6-10). I am not sure of the specific circumstances because it is not easily replicated.
I usually only use the trackpad, because I am just typing. But sometimes I will plug in a USB mouse for a while.
This is what happens.
The system continues working but does not respond in any way to the mouse, trackpad or keyboard. So it is essentially frozen, except for whatever was started when it happened.
The only way I have found to get out of it is to hold down the power button to reboot. This is asking for trouble, not least because I am usually running a Postgres server on my machine - worries about database corruption though it has never happened yet.
So right now, I was watching a YouTube video, plugging the mouse in and it happened again. YouTube happily continued playing the video, so its not like the computer is frozen, but its peripherals are locked out.
It's hard to tell from looking at the Console app, because there is a lot of stuff going there and you get all the diagnostics from the booting up sequence. But I usually spot a USB related messages like this one.
2015-08-15 2:48:43.000 PM kernel USBF: 264266.931 AppleUSBHubPort: Port 3 of Hub at 0xfa100000 about to terminate a busy device (USB Device) after waiting 10 seconds
(btw how do I run the console app from the command line? sudo dmesg? doesn't seem to print out the same things at all).
What could be causing this? The same mouse will work on the same port after reboot. I am not sure if it's one particular mouse, I don't think so. This has happened over a number of Mavericks maintenance releases, so it seems to be a persistent "feature" of my machine, not tied to a glitchy Mavericks update.