If you really like DVR functionality, apps are generally subpar to a good (hardware) DVR. d21mike summarized a number of streaming services with software DVRs but if you look into them, you'll find limitations & shortcomings atypical of the hardware DVR experience. For example, some software DVRs have time expirations (watch within X number of days or the video auto-deletes). Like to skip commercials? I'm not sure any of them will let you do that. Some services have DVR support for only some channels. Etc.
Nutshell: from all I've read & heard, software DVRs still have a ways to go to match up well vs. hardware DVRs.
If you really love DVR functionality but are increasingly attracted to the (sometimes perceived) lower pricing of streaming, I suggest looking at aggressive offers from players like DISH. Their 2-year price lock with one great (hardware DVR) is very competitive against any of the streaming options... and that comes with a real DVR, generally better HD video, 5.1 surround sound instead of just stereo or mono, etc. With the Dish Anywhere app, the service streams well to any iDevice too, whether home or away.
In my experience, when one assembles the channels & shows they really like (in a legal way), what they are spending tends to be close- if not more than- getting a "fat" bundle with an offer like theirs. Then, one needs to potentially jump app to app, or even box to box to watch what you want, without an at-a-glance, on-screen guide that includes everything, and any dollar "savings" just doesn't seem to be worth it... especially if you have to train less tech-savvy family members to hop app to app and box to box too.
I think streaming works for some people. But it sure has many disadvantages right now. From my own perspective, the loss of 5.1 surround + DVR commercial skip + comparable HD picture quality, etc. is too much. Even if I could save $15-$30, stuff like that is well worth the extra to me.