This is such an interesting topic...
I find these success stories very intriguing! For me, if I was single, I think it would be a no-brainer. Unfortunately, it seems like every single one of my wife's shows aren't available on iTunes yet. Some of them I can get over HD Antenna now, but others (Food Network, HGTV, DIY) are frustratingly absent.
Until iTunes increases its content numbers on some of the more niche stations, I don't think we'll be able to make the switch.... buy boy do I look forward to that day! Then again, maybe we need to re-think how much TV we watch, just get a few subscriptions and live with it. I don't know. I think another hurdle to prepare for would be the massive influx of content taking up hard drive space. I think a fairly robus RAID Hard Drive solution would be in order for this type of thing... but many people aren't aware of these types of things.
Is there anyone out there who has cancelled their cable, and not been happy with the transition to AppleTV? Seems like all I've read so far is "good news!"