a tv tuner wont rec 2 channels at the same time tata sky+ would
a tv tuner would need the computer to be on all the time for recording tata sky+ wudnt (the STB just needs to be on standby)
the quality of the recording on tata sky+ would far exceed that of the tuner
the scheduling for rec would be more easier on the tata sky+ given the guide
as for the extraction part wait for some time ppl are trying things out and it would be possible to get the files out of the hard disk in the STB and transfer to PC
i myself am trying to do so will post if i succeed :S