(This HAS been posted before, but not directly in feature suggestions.)
I have multiple ways that I get shows and movies and here are reasons why I think Roku should add a "Viewing History" feature.
I have seen literally thousands of shows and movies and I do not have an encyclopedic memory. By keeping a spreadsheet of everything I've seen (and when) I am able to access this data from anywhere and know if I have seen something already.
Maybe I'm browsing movies and something sounds interesting, but familiar. A quick check will verify whether I've seen it already. (Let's face it. Some movies are pretty forgettable, and before I kept records, I might find myself 20 minutes in before realizing I saw it already,)
Keeping track of show seasons can be important when a service drops a show that another service picks up. Now where was I....
Sometimes I am at the library browsing DVDs of shows or movies and the question comes up.
The more I use Roku to stream, the more gaps appear in my data. (Although I can watch Netflix through Roku and still get viewing data from Netflix.)