This has only happened to me once, and only when connecting my Sansa Clip 1GB via USB.  On the other hand, I don’t often connect the Sansa Clip so it could be a common problem for some.  I’m running the Asus P5K-VM motherboard (Intel G33/ICH9).

Basically, after connecting and connecting the device a few times, I got these lines in the output of dmesg:
[268429.607723] usb 8-2: new high speed USB device using ehci_hcd and address 10
[268431.894349] ehci_hcd 0000:00:1d.7: port 2 reset error -110
[268431.894356] hub 8-0:1.0: hub_port_status failed (err = -32)
At that point, I could not get my computer to recognize the Sansa Clip again even after powering it on and off and reconnecting the USB cable multiple times.

I was determined to resolve this problem without rebooting, as I hate rebooting (as I’ve explained previously).  I was able to get it working again by entering the following commands:

sudo modprobe -r ehci_hcd
sudo modprobe ehci_hcd

After that my USB keyboard (which had been plugged in the whole time) mysteriously started typing the enter key continuously until I pressed a different key, at which point everything seemed to be working fine.