I have FIOS and absolutely love it. The picture quality is tremendous and truly does blow away comcast.
That being said, a few things to keep in mind:
1. To get FSN HD, make sure you order the "EXTREME HD" package, not just the "HD package". I think it's an additional 12-15 channels; (includes HD versions of FSN HD, but also Travel channel, SPEED, Food network, and the HD versions of the Disney channels for anyone with kids.) Well worth it and more important, the ONLY way to get FSN HD.
2. The "multi-room" DVR is a bit misleading. The "multi-room" option only works on NON HD tv's. For example, I have 4 verizon boxes; 3 HD boxes and 1 regular box. If I DVR something on one of my 3 HD boxes, the only tv in the house I can watch it in "another room" is on the traditional box/old television. The HD boxes do not have the ability to be "multi-room", only the traditional box. And since the DVR is on the HD big screen tv, I can watch the recorded program on either the 52 inch HD set, or the old 19 inch "walmart" set in the basement. Something the commercials totally mislead you about.
That being said, would highly recommend FIOS if available in your area if for no other reason than to get out from under your cable company!