This I think would be really a very neat, yet simple feature to add. It won't really take much work but would be really useful..
When a person visits a user account address(eg mine - alvasrawuther.dropmark.com) to view their portfolio - the person is led directly led to the user's collection(if it's the only one) or collection select splash screen(if there are more than one). And that it displays only public collections. With a small 'Sign in' click at the bottom only as prominent as the 'Powered by dropmark' link.
It's a small change, but it'll mean a huge difference for me and many others who use a collection as a portfolio sometimes.
Thanks, I hope that you'll consider my suggestion.