Salesforce and Force.com in general are attracting increasing numbers of users, and therefore more and more administrators and developers are cutting their teeth on the platform and many have been using it for many years already.
Due to the nature of the platform, development can range from configuration (declarative development) which requires no code to be written, through to custom webservices, pages, and database triggers. Nearly all complex solutions require a mixture of the two styles, and even working out where the line is can be part of the challenge. Because of the two distinct areas of development I believe a Salesforce exchange site would be beneficial for many people because the questions don't really fit in at stackoverflow.com every time.
For instance, today I answered this question:
which could relate to code, but if the requirement is just that a report is needed then no code is needed, making it a bad fit for the site but not leaving the asker anywhere sensible to turn. Granted code based questions would potentially belong on stack overflow, but a lot of the time the asker may be an administrator, and part of the skill set is knowing if code is required, and avoiding it where possible!