Well, if you want the ultimate in power/features, myth is the only way to go (and it's free). If you want the easiest install, I'd try one of the livecd's. Or just rent a pvr from your cable company. My cable company rents pvr's for $4 per month that allow you to record stuff and play it back whenever. If you think about it, a dual tuner card is $120. That's 30 months, or 2.5 years, of a pvr from the cable company.
Really, if you just want basic pvr service, it's cheaper to rent a dedicated unit. MythTV does quite a bit more though.
My system is in 2 units. I have a backend in my bedroom which also has a tv out to a tv in my bedroom. I have that connected by ethernet to my house network. My TV in my living room has a frontend connected to it that gets streamed video from my backend in my bedroom. Both systems connect to my fileserver in my office. The backend stores the live tv recordings only. The fileserver holds music which is played by mythmusic (as mp3's), dvd's I ripped into the system, photos from photocd's so I can show them in slideshows, and roms for the video games I play (mythgame can emulate nes, snes, atari, and arcade machines using mame).
I also have a browser installed with mythtv, a web server so I can access my system from any computer in the house and set up what I want to record etc, a weather module that gets my local weather and shows it whenever I want, and a webcam based video conferencing module.
I also have mythfrontend installed on all my computers, so I can watch live TV or recordings on any of my computers while I'm doing stuff on the other computers nearby. This turns every computer in my house into a tv or dvd player, video game system, cd player, slide projector, video conferencing phone, etc. Plus I don't need to duplicate storage... mythtv is the only pvr I know of that allows you to centralize all the information in one central location and then stream that to whichever front end you want, saving you a lot of space.
Storage and number of tuners is another factor. Kaltag has 2.4 terabytes of storage space on his system. Basically, you can have as much as you want with myth. You can also have as many tuners as you want. Some people have 10+ tuners recording stuff. I personally have 2 and about 320mb of storage space, which I find to be sufficient, but I can easily expand when I fill it by throwing another hard drive into either my mythtv backend or my file server.
If you feel you want a system like that, you need to go with mythtv. If you want a basic pvr, rent it from your cable company or get a tivo. It will be cheaper anyways, and easier to set up.
