WHAT I DID...
Here's what I have decided to do until Tablo gets the "keep X episodes" feature (or even if it never does):
I reactivated one of my old TiVo Premiere boxes along with my old TiVo Stream (it lets me watch live & recorded content on my WiFi devices like the new Tablo). I had added a 1TB media drive, giving me 1.5TB total on the TiVo Premiere (compared to 2TB on the Tablo). I also have TiVo's Slide Pro remote that has a lighted slide out keyboard which makes searches waaaay easier. It is Bluetooth so I don't have to point it at the box.
I am still using my Tablo to record all of my movies. I am also using it for the handful of shows that I want to keep ALL episodes of (Seinfeld, Survivor, The Aviators, and Raising Hope). On my TiVo, I only record the shows that I want to keep only the latest X episodes of (news, game shows, sitcoms, reality shows, etc.).
Although TiVo is costing me $19.99/mo ($14.99 with 1 yr commitment) it is worth it to me to avoid the hassle of constantly deleting old episodes on the Tablo. Unexpectedly, I've discovered that I prefer the TiVo interface over Tablo's Roku & web apps. I have Amazon, Hulu, Netflix, and YouTube all in one place with TiVo. Tablo's Roku app crashes routinely and the Tablo web app doesn't play well with my Apple TV (though not Tablo's fault). Make your own comparison but for features, ease of use, and reliability I call TiVo the winner. I just hate paying their high monthly fee which is why I originally switched to Tablo.
If Tablo doesn't get the "keep X episodes" feature by this summer, I'll probably go for the annual TiVo subscription for $14.99/mo. I feel I must always keep the Tablo as I already paid the $150 for the lifetime guide subscription. Looking on the bright side, I'll have 3.5TB of total storage. I will keep using the Tablo for movies and complete TV show series as its 2GB capacity is about 300 hours of HD content. I'll eventually drop Hulu and Netflix (but will keep Amazon Prime to have recent movies, music, and 2-day shipping). I'm currently recording full series of my favorite network shows on the Tablo, so I won't miss Hulu. Believe it or not, I rarely use those pay streaming services at present because I get 19 worthwhile OTA digital channels (not counting the Spanish, shopping, & religious channels). I am in Austin, TX with a Mohu Leaf antenna in the attic. It is connected to a signal amplifier and wired to all of my existing cable outlets in the house. My future plan is for my total home entertainment costs to be only TiVo + Amazon. I know that I will still have more variety and content than I can watch in a lifetime. Of course, I will also have the MLB and NFL pay services for my sports addiction.
To sum things up, TiVo is a good alternative to Tablo. You pay roughly $10 more per month for the guide service with TiVo (you can't record on TiVo without the service) but have a nicer, full featured interface. Equipment prices are comparable.