I would like to link a logo to paypal for gift certificates and it's asking for the URL. What is the URL for Ubuntu One's folders?
https://one.ubuntu.com/ is the URL to the base site.
If you want to 'publish' a file you will click on 'more' at the right of the file name. Then click the option to publish it. When you do that you will see a URL that the file is published too. (see below)
I hope this helps with your question.