After doing some research on stackapps.com (thanks again to saiarcot895 for the tip), I finally found what I was looking for, namely an easy way to get notified about new answers, posts and/or comments for the topics that I am interested in and are listed on askubuntu.com and all the other places from StackExchange network.
The application is called StackTracker (a Cross-platform desktop notification app) and it can be used natively in Windows and Mac OS X. If you want to use it with Ubuntu/Linux, you need to install Wine and start this app using Wine. The official page will provide you with a download link for a Linux version of StackTracker but there is no Linux package in there only a fake link. I may be wrong but I was not able to find any package built for Linux in there.
StackTracker can be found and downloaded on this page, and it won't require users to actualy login or enter a password or things like that. The application displays a task tray notification when someone has posted an answer or a comment to a question you are tracking on any of the StackExchange sites. Clicking the notification will open the corresponding question in your browser.
Already tested it in Windows and also in Linux (via Wine), and it works fine. It uses very few resources if any.