i'm in the UK and i really want to do that too! how?!
Well here in the UK we can easily record 20+ DVB-T standard digital terrestrial TV channels concurrently while watching 2-3 channels live and or playing a ripped DVD. Our Cores are typically 3Ghz Celeron's with 512mb-1Gb RAM and are typically based on i945 class motherboards. With this kind of level of activity at the core we typically see less than 30% processor usage. Obviously recording 30+ channels concurrently is not a likely scenario in normal domestic usage... but it gives you some metric on the capacity to load up a system.
Hope this helps
Not sure what part of the planet you are from HugoLP, but in the US a satellite card won't work with our only 2 (small dish) satellite providers. Not yet anyway, and not in Linux for some time I'm sure.
Sargenthp, you won't have any problems with most modern drives and 4 tuners simultaneously recording. 2 PVR-500s work just fine in standalone MythTV. Actually I have 4 HD streams recording at the same time, that is probably as close to maximizing disk I/O as you can get without constant recording "blips"; every once in a while during fast moving scenes I do get "blips" when all 4 were recording at the same time.
What you will have problems with is how fast the system fills up