Leah Messinger at iMediaConnection has a worthwhile article debunking 9 popular widget "myths."  Some of here more important points, in my view:

• US companies will spend $40 million in 2008 (up from $15 million in 2007) to deploy widgets
• media companies and brands are becoming increasingly comfortable with user-mediated content so the industry is likely to see the widget business expand far beyond social networking
• contrary to the popular notion that there's no room for ads on widgets, widgets, in effect, are ads   
• typically, if a widget isn't viral than the publisher hasn't done a good job

There are many other good nuggets in the article, so check it out.