I used to use a pc for pvr but I got tired of it and it never really worked as well as the tivo has.
For the monthly fee all you really do get is tv listings.
Theres some other perks like being able to admin your tivo over the net, but thats possible with htpc also.
Theres a few tivo apps that I really like.
One is tivo dot net.
Its a real time transcoder that will let you watch anything that your pc can play on your tivo.
Really for me its a convenience thing.
The tivo is small, quiet and can record two channels at once.
I can stream video over the network to it and it just works.
I can transfer recordings to my pc and save them to dvd, or a portable.,
A htpc can do all this but it was a hassle for me to get it to work like I wanted I got tired of trying. Tried Mythtv, beyondtv, gbpvr and everything out there.
The plug and play of it is the reason the fee is worth it to me.
That and I got one of the refurb units that comes with a monthly fee of 12.95.