More specifically, it doesn't necessarily guarantee that one is "on the internet". There could still be a connectivity issue where you don't really have internet access. It specifically means that the modem is in block sync mode with the CMTS/system if it is lit *SOLIDLY*.
According to the manual (and most, if not all other modems I've ever seen) the "Online" light should be lit steadily (regardless of the color and should not blinking) indicating that the modem is in sync mode with the Comcast system. Only the "Link" light may or may not be blinking depending on a particular modem's firmware load / instruction coding and in some cases, the level of activity. Sync mode is a MUST in order to have connectivity to the internet.
I have this modem and the "online" light blinks orange. All other lights are solid green. I'm getting 52 mb down on the blast service and everything seems fine. SOme people are saying this light should be solid????
If you have the 722G it's normal for the "link" light to flash orange with a 10/100 ethernet connection. Look again at the lights, are you sure it's the "online" light?....The "link" light should flash green with a 10/100/1000 ethernet connection. The "online" light should be solid green when online.