I already searched the site, but I could only find answers relating to using GPL libraries in software that people were going to sell/distribute. In this case the answer is that they must also make the source code available.
What about SaaS? That is, I'll be building an app that clients will pay a monthly fee to use over the Internet, and they won't download anything or get access to the code.
In this case am I allowed to use full GPL libraries without having to make my source code available?
Is there some other restriction/requirement of the GPL that I should be aware even if my model is SaaS?