We are considering entering the hackathon, but the below criteria provides for some interesting grey areas: 

The application you or your team submits must...
...have been developed solely as part of this Hackathon 

For example:

• Can we re-use code we have written for another related product?
• I know we can use open-source libraries and APIs, but what about an API to our own pre-existing product?
• What if we were want to modify an existing project to be an entrant into this Salesforce contest?
• Lastly, what if someone had the idea or started tinkering with it a year ago, but now wants to finish it in the hackathon?

Sorry for the baragge of questions...the word "solely" is just so absolute. Most people who are entering this have probably done some work on their idea apart fro this hackathon.  My question is how much "prior work" or "non-hackathon" work is acceptable?

ps – This is a continuation of a comment thread here – I thought it warranted its own thread after considering it further.