The Pi2 is now available and has a bit more power. I doubt a Pi would be up to both recording and playback. I also have some doubts about playback with MPEG2 OTA signals. There is a HD HomeRun that does MPEG4 transcoding so that is an option.
I've tried several devices for OTA and the best luck I've had is with a low end AMD APU solution. A suitable motherboard and APU can be purchased for about $150. Add a case, RAM, hard drive, cheap MCE remote and O/S. (A DVD or BD player is optional. Use a flash drive to install the O/S.)
NPVR is another good software solution for recording and playback of OTA using Windows. There are some preconfigured Linux solutions as well.