I have FIOS running with my Replay 4504's and a pair of Motorola QIP-2500's, I think. It works great.
The Replays control the FIOS boxes via IR blaster. It's reasonably fast compared with the old DCT units I had years ago last time I tried digital cable. In other words, when changing channels, the old channel doesn't go away until just before the new one appears. There is no blue screen or anything like that.
I can't remember what IR blaster setting I used. The Motorola QIP series doesn't show up on there at all, as I recall, and I think I just used one of the first Motorola boxes that were listed, it sounded common, and it worked fine. Still does.
This is the first time I have had to use the IR blasters (based on my old experiences with cable boxes I hate them) so they are a little annoying. From time to time the IR blaster would fall off and then I tape a bunch of crap. So I fixed that with metallic duct tape. They don't come off anymore.
The guide is pretty accurate. For my area (Falls Church, VA) the Verizon FIOS is one of the options, which was a nice surprise. Some of the Spanish channels were swapped (World cup time was annoying, but who would ever try to tape a soccer game, it's tough enough to time football). Everything else there seems to work fine.
The data side is simple. FIOS ran a 100BT ethernet port to the middle of my house. That goes into a router and a switch. The router they gave me (DLink) worked fine, and it's sitting there in case I ever decide to try it. I have a Linksys running DDWRT instead. If you use Poopli or whatever you would have to open some ports in it to forward to your Replays, duh.
Data interface to the world is PPPoE instead of DHCP, which is annoying. I hear that some newer subscriptions are provisioned with DHCP instead. That takes less overhead and would probably make my router work better, so I'm looking forward to it.
There's also a NIM box, which is used for the VOD. That's the only thing I sorta don't like, I can't easily record VOD as they don't show up on regular channels. But I don't have much reason to record VOD anyway, since it's on whenever I want and has FF and RW buttons. The only problem is sometimes shows will expire before I have a chance to watch 'em.
FIOS has had some problems with VOD. Vendors offer a lot more shows on VOD than Verizon has been offering, which is kinda annoying. Go look on Showtime's site and compare that to the VOD offerings. Anyway, that's a bit out of scope here.
The short of it is, FIOS works fine with my Replays. I like it a lot better than I did Cox, since all the channels are quite clear. It's also cheaper. With Cox I had the analog service, now I have digital with two boxes and much better picture and network speeds for the same price. Actually two bucks a month less, I think.