Over the month I have received reports for co-works that the internet becomes unbearably slow for short periods of time. I was in the office yesterday, and was able to experience this phenomena http://stage.results.speedtest.comcast.net/result/286585992.png.
This would be opposed to what I have come to consider our peak speed http://stage.results.speedtest.comcast.net/result/286917332.png, which is of course no where near what you'd expect from "EXTREME 105".
Additionally there has been an increase in constant packet loss. I've tested this outside our internal network, just running directly from the Comcast gateway.
Also I've had DNS issues since our switch to Comcast. Ping 22.214.171.124 & 126.96.36.199 generally returns "Request timed out", with a few (less than 10%) making it through with > 40ms.