Not in house but...
Not long in my current IT Manager role, and with an inherited 2MB leased line to the 'net we had similar issues with our entire connectivity grinding to a standstill. This included the RD connections for two factories so was a critical failure.
Frantic sorting through traffic statistics and logs from the main Cisco device then checking round the building traced it to a TomTom device update. I figured out roughly what was happening, the SatNav would request an update packet from the servers at Akamai; if it didn't receive the response in a certain time it would assume packet loss and resend the request. The update server would happily service both packet requests though and with a slow connection neither would be received in time so the device would send another request for the same packet, slowing things down more; repeat, rinse and recycle ad infinitum. Once the device was disconnected and the multiple update packets had worked through the system everything returned to normal. I was able to then justify adding a backup ADSL line to use for any updating.
The same user had a habit of leaving the Sky home page running on his computer, the video playing constantly also impacted on our traffic levels until I told him to stop. More recently we've had an issue with the standard IE* home page hitting the CPUs on the Parallels servers but a GPO change to force the homepages to an internal site cured that.
*We have to use it for legacy apps.