Interesting dx-spots will be forwarded to the OS-X Notification Center and to Growl. If you use both, you may deactivate one service to avoid double notifications. While Growl is always active, the OS-X notifications are displayed only, when RUMlogNG is in the background.
You have to switch on Growl in the Preferences under the DX-Alarm tab.
In the Growl preferences you can set further options. An interesting feature could be the possibility to push spots to your mobile phone using Prowl.
Some Growl display allow a feedback to RUMlog. Clicking in it will transfer the spot data to the logging mask and the trx will be tuned.