The notifier feature in RSSOwl is capable of informing you as soon as news are downloaded. It can easily be enabled from the "Notifier" entry in preferences. Enabling this feature will show notifications for any downloaded news from all of your subscriptions.
Now, consider you only want to be notified about news that match a specific search (e.g. all news that contain a certain word or where the author is a specific person). Simply create this search as "Saved Search" with the desired conditions and set the Notifier to only show notifications for this search in preferences.
As soon as News Filters are implemented, this feature will even be easier to use.
Stay tuned for milestone 9!