Yes, we should keep an eye on them
Spam is bad for the site, it does not help anybody and it clutters all those good questions and answers we have here.
No, we should not flag and delete them all
These are my personal criteria that I keep in mind for cases where I may welcome a self-promoting answer, and I also upvote them:
- it does answer the question and helps solving an issue.
- the application was free and Open Source.
- the answer was more than a link only. It should at least explain the benefits and ideally give instructions on how to use it (screenshots are always great).
- the software is available for Ubuntu, or was specifically designed for Ubuntu.
- an installer for Ubuntu was provided (e.g. DEB or PPA)
- in some cases (that did happen!) the application project was initiated following a question here. Then of course the answer given would be the ultimate and best solution we can think of. That would be Ubuntu and Ask Ubuntu at their best!
The more of these criteria are met the more should we not be too harsh on self-promoting a good, free, and voluntarily initiated software project.
Very rarely, and for some very problematic issues even a closed source, or a commercial solution can be the best answer. In these exceptional cases it would not help anybody if that answer disappeared, but we should not allow self-promoting just another application on a given topic.
