I have had FIOS TV for almost a month now.
The HD channels are definitely not compressed to the level they are on the cable systems, as Verizon has much more bandwidth to spare than the cable operators.
Along with the Internet (15 down, 2 up), it is a bit cheaper than my former cable bill and the Internet is faster.
I also do not have any artifacts or pixelation on HD channels, an annoyance I dealt with on cable.