Gold Duke of Edinburgh - Worth Doing? Watch
Just remember that you shouldn't just 'list' this sort of stuff - you need to explain why you did it and what you got out of it, ie. training for a 5k shows determination, working to a goal/deadline, a sense of achievement/pleasure when you did it plus an understanding of community/social responsibility etc etc
It might not be much in itself, but it would help if you can do subject related volunteering and skills. The expedition is a laugh as well
This is the best answer by far in this thread, but I can also tell you that the DofE is considered the best non-academic qualification for University applications and for jobs in the future. Have a look at the DofE's own website at the companies, colleges and universities that endorse it as part of their Skills for Work campaign. More importantly it will stand you in good stead for life.
DofE is not highly regarded by universities and is far from the best non academic qualification for the vast majority of applicants. There's almost always something available that would be more subject relevant (even if non academic) than DofE.
Find me a university that states clearly on their website that DofE is desirable in applicants and would directly increase the chances of receiving an offer.