I know one professional matchmaker who is well-known and successful in his business and he told me he watches 30-40 pro fights in a week, since that is his job. For me, it is between 0-10, I'd say two or three is the average. There are weeks I don't watch anything or I can sit through an eight-fight card
I watch pretty much all of the HBO/Showtime/PPV cards and I'll check out a guy fighting if I hear he's a good prospect... Other than that, If I happen to see it, I'll watch
I'd say about 20 fights a week. Normally a UK bill and then a US one. Throw in the occasional Russian, Japanese, Mexican or German card. This weekend I watched the Lebedev card from Moscow, Abraham vs Smith from Germany and the Montreal card, with Beterbiev vs Cloud.