I think it's a bit more than just TV listings. I've only had Tivo (from Virgin Media) for about 3 weeks and I can't remember much about the original Tivo having only seen it on sale in a shop when it first came out, but I gather part of the Tivo service is things like programme suggestions based on what you watch.
For instance, if I record Family Guy it'll suggest American Dad for me too. If I record Corrie it'll suggest Eastenders. I think it also will find things like films and TV programmes based on actors in shows that I've already recorded, similar shows and shows that 'Virgin' like (not sure if that is Virgin staff, Tivo staff or a back hander from a TV company).
I think I pay about £3 a month at the moment for the Tivo service as I've only got the basic M+ TV package, but for that it gives me a PVR with 3 tuners, a 500GB hard drive and HD capability (and other bells and whistles which I've yet to really play with). As it happens I also have a PC setup with MythTV and a couple of Freeview tuners, but for the non-technical it's not a bad service and from what I can tell better than Sky+/Sky + HD if you're in a cabled area.