Not many people, and those that do overestimate how many people actually own one. It's a near-infuriating debate that I've had multiple times, with multiple people who believe too much in cassettes and cassette culture. Don't get me wrong, I enjoy them and the scenes that still use them but it's like talking to a wall when trying to convince people otherwise.

Anything on tape is available somewhere else better that's a lot more portable...

This is mostly true. Some noise stuff is very hard to come by, as bfv points out. The same can be said for certain drone influenced music as well as some garage rock. Many bands and labels that primarily do local shows offer cassettes, so if you want something at a show at least you get a digital download card with it.

T-Dog they're not too expensive (unlike LPs) and I should have noted this earlier but in our case we allow the bands to decide which media they'd like to be released on (CD or Tape). As far as selling them, there hasn't been a noticeable difference between the CDs and Tapes we've put out. I'd imagine that this is because of the scale (run of 50-100) and the fact that each purchase comes with a digital download.