I had FiOS installed on Saturday after being a long-term Comcast customer. I have not cancelled my Comcast service yet and am seriously considering dropping FiOS and returning to Comcast.
Installation went well, a bit longer than expected but no major glitches. Less than 2 days later, I lot my Internet, but since this is a new service in a new neighborhood I was willing to give Verizon the benefit of the doubt. When the tech came by the next day to fix it (which he did, btw), I told him that I had since upgraded my service from the initial 15 Mbps service to the 50 Mbps service. He promptly told me that I would never get the 50 Mbps speed because the way FiOS is installed in my condo, the fiber does not go directly to my unit, in other words "the last mile" is twisted pair copper. The best I might get would be between 20-25 Mbps. When I last tested my Comcast speed on the day of the installation I was getting 25! So I'm paying for 50 Mbps and getting only half that speed.
This was obviously a major bummer and could be the dealbreaker. As for the TV, I don't see any discernable difference in quality between the picture I got with Comcast and the picture from FiOS. That's not a dealbreaker in itself but I was expecting better.
Lesson learned: Do your homework before installation! If I had known that I wasn't going to be able to get 50 Mpbs (what I am PAYING for!), I definitely would have reconsidered.
As it is now, I'm seriously questioning any long term commitment to this service. FiOS is not all it's cracked up to be. You really have to read the fine print and do your due diligence.