Career Notify tracks your Facebook friends' changes in their jobs.
Job Change Notifier finds changes in your LinkedIn connections' work experience. (Update: Due to changes in LinkedIn's API this service has shutdown.)
Both of these will send you an email when something changes. It takes the needed work out of watching for changes on your networks. I have used the LinkedIn one for a while and it has proven it's worth and I just signed up for the Facebook version and am sure it will be as useful.