I can't speak for Comcast, but my FiOS boxes allow for you to turn off the initial launch/guide ad popups in your box settings. It's not the easiest of settings to find, but it's there (and enabled by default, of course). Call support (fast and helpful...not kidding) or search the online support area, which is how I figured it out and was easy to find the answer. The only persistent ad, I believe, is a single ad bar (annoying, but doesn't obstruct view) at the bottom of the channel guide, used mostly (from what I recall...I don't pay much attention to it) for promos of new on-demand releases. Love LOVE FiOS.