I have the 4 tuner Tablo as well, and while not perfect, I'm not experiencing anywhere near the problems y'all are having. Since the early days of Tablo, I upgraded my antenna and router, and it's been pretty solid ever since. There are a couple of issues, though, that I've learned to live with... the first is the dreaded crash, and there are a couple of ways that can happen. With a very weak signal, or total loss as when a transmitter goes offline, Tablo will crash. Also, Tablo can be susceptible to ESD, so I've learned to avoid touching the underside front edge, where I used to check the "warmth" of the unit. Tho it gets very warm to the touch, I have it standing on edge, and haven't had any issues, other than those noted, in 3 years of heavy use.
The other issue I have is occasionally being kicked back to the guide while watching live TV. When no recordings are going on, like during the day, I haven't noticed the problem. It's mainly at night where a couple of shows are being recorded, and maybe I'm watching one. So, what I do is wait until the recording starts, and then immediately start watching the recording, and I don't see the problem then.
Other than that, the Tablo has been very solid for me, never missing recordings, and I record a LOT of programs, more than I can possibly watch and it never misses. So, I suspect either an issue with the guide data, or maybe an issue where the Tablo is set to record only new episodes and the show is either a rerun or mistakenly not tagged as new in the guide.