What is the policy regarding "bumping" unanswered questions? Is this taboo?
Well, it's sort of covered in the faq:
What if I don’t get a good answer?
In order to get good answers, you have to put some effort into your question. Edit your question to provide status and progress updates. Document your own continued efforts to answer your question. This will naturally bump your question and get more people interested in it.
Of course bumping by answering them is the most awesome solution of all. :)
Feel free to edit the questions you answer to make them more useful, as well.
If you don't get a good answer or any answer at all, you can always offer a bounty. But updating a question with additional information and progress updates is also a way to gain notice.
Posting an update merely to "bump" your question would be discouraged. Updating to provide an actual update, updating by providing an answer or solution, or updating by offering a bounty would be encouraged.