Since you're starting out I recommend you plan on keeping your cable for a while. HTPCs typically require an immense amount of time to configure. If you're not PC savvy you're in for a possibly painful process.
Netflix can be a problem. They are forced by the TV/Movie groups to actively protect their streams. This means that any free software such as XBMC (inherently insecure - anyone can download the source) will not be able to use Netflix. There are addons and some of those may be able to do Netflix, but I wouldn't count on it as a reliable source for video.
I use XBMC and I found that it works really well for content I already have (ripped movies, downloaded shows, etc). It hasn't had the ability to act as an over the air DVR though work is progressing in this area. You can set up a central MySQL database that all your XBMC clients can use, so putting a client at each TV is very doable. XBMC doesn't really work as a streamer to other devices such as trying to watch a show on your phone. Again, work is happening on this, but if that's a important need XBMC isn't what you want. Look to Plex for that.
As for dumping cable - this really depends on what you watch and what you're willing to do to get it. It has taken me about a year to finally convince my wife we can do without Directv. We want to watch stuff as soon as it comes out and sometimes that stuff isn't available for weeks if ever on Hulu/Netflix/etc. After all that there are a few obscure shows we will end up doing without.
I now have several programs I've written involving a seedbox, Tivo DVR, NAS, etc to collect content in a central location. Even though it is automated, it still requires a significant amount of maintenance and monitoring.