My stance on this idea has always been the same, no matter what technology has come along: I freaking LOVE the idea, but I personally watch far too much TV to make it feasible for myself.

So essentially, it all comes down to how much TV you watch, and how much it's worth to you to have more discovery (not the channel). For example, when someone says "oh, you should check out ____." With a DVR you can just set that up for no additional fee. But with pay-per-watch, you might be extra hesitant to watch something new if you know that it'll cost you a few bucks.

If it works for your specific use case, I say go for it. For me, I want the DVR for all the shows I watch, and for live events.

*edit*
Plus, we only pay around $50 for the basic Verizon FIOS package, which includes a very decent number of channels (90% of which we'll never watch, of course).