Since I figured out the hidden dual buffer feature the only thing that really annoys me with the FIOS DVR vs my DTV dvr is the inability of the FIOS DVR to save anything currently in the buffers. Example I am watching a 30 minute program and 20 minutes in get called away and forget to hit record. I come back and the program has ended but is still there in entirety in the buffer. With DTV I just rewind into the program and hit record and it is saved, with FIOS I am told I cannot record a program that has already aired.
When the original TIVO for DirecTV box came out it had a feature that users grew to love called dual live buffers. Since the device required 2 connections and tuners so you could watch a program on tuner A while recording a different program on tuner B it basically kept dual 1 hour program streams you could switch between so you could be watching program A on tuner 1 while program B on the other tuner was also being buffered and you could switch back and forth between them. When DTV broke away from TIVO and put out their own branded DVR's the number 1 complaint from subscribers was the lack of similar capability on those DVR's. They eventually relented and in fact improved upon it slightly by making each buffer 1.5 hours long.
In another thread on this topic a year or so back on this forum I said that was one of the deal killers for me cutting the cord with DTV, the other being the NFL package. I have since discovered that the "feature" is actually there if you use the "Previous" button. I don't know what button this is on the FIOS remote but on my Logitech it is the previous button which switches between what you are currently watching and whatever channel (or recorded) program you were watching previously. Example if I am currently watching 507 and had previously been watching 505 if I hit the previous button it takes me to channel 505 and I can rewind back through however much there is in that buffer, hit previous again I am back on 507 without resetting the buffer so I can rewind 507.
With the FIOS box there is one little wrinkle not present with the DTV box in that the previous button always takes you to whatever activity you were doing previously so if you happened to be watching a recording previous to changing to 507 and hit previous it will take you back into the recording. The interesting thing is that if before watching the recording you happened to have been watching 505 and are currently on 507 if instead of hitting previous you re-enter 505 it will change to 505 with whatever was in the buffer just like using the previous button. I hope that all isn't too confusing, it sounds more complicated when I read this than it actually is in reality.