I began my programming career in web development using PHP and MySQL. I got quite accustomed to utilizing db for storage of most dynamic data as well as some setting/parameter data. Sometimes there would be a lot of data while other times entries in the tables would be few. To me this just seemed natural and as far as I'm aware this is more or less an acceptable approach in web development. (Please correct me if I'm wrong...)
I'm delving into desktop applications now and my natural inclination is to again utilize a db to store a lot of information that will be generated through the usage of the application.
However, as far as I can tell I don't see applications (that I use) utilizing a db very often. [EDIT: It has since been pointed out that this was a faulty assumption in that many applications do use lightweight dbs embedded into the program itself.] What is the reason for this? At what point is it appropriate to utilize a db? Are there any standards on this matter? Also what are the reasons to NOT use a db to develop a desktop application?