Read/Write Web explains why 2007 will be the breakout year for RSS, and it comes down to two things - first, Internet Explorer 7:

Despite the issues with RSS implementation in IE7 which Marshall Kirkpatrick rightly pointed out - and Dave Winer agreed with - IE7 still represents a major milestone for RSS. It will almost certainly be the most used browser in the world within 12 months

Don't underestimate the impact IE 7 will have here. It's still the most widely used browser, and it will stay that way for the forseeable future. I'm already seeing an uptick in IE usage in my logs (on the RSS side) due to the slow rollout of IE 7 beta. This is one thing that will help make RSS mainstream. The other - Outlook:

"Work with RSS Subscriptions from within Office Outlook 2007. You can now fully subscribe to and interact with Really Simple Syndication (RSS) feeds right from Office Outlook 2007, the most natural place to manage this kind of information. It’s easy to get started adding RSS feeds using the RSS Subscriptions home page within Office Outlook 2007."

Personally, I hate Outlook a lot, and won't work with it (I tried recently - I still hate it) - but I'm an outlier on this. Outlook is used by tons of people, and having built-in RSS support is going to really drive adoption, IMHO.