Specific advice to the Guardian: I'd encourage you to take the above generic advice.
When visiting the mobile site, you're initially greeted explaining it's a beta, and there's a link in the greeting to offer feedback. I dismissed it and started browsing, and intended to report a bug -- but then the feedback link was nowhere obvious, so I figured someone else would eventually look deeper.
The bug in question in case it's not reported yet: the very first article has a title that overlays the date when browsing on an iPad in portrait mode. (You should be using min-height somewhere instead of height, or worry about headline lengths.)
PS: Thanks to your feedback, I reported to my colleagues the fact that we may want to give our beta/alpha readers a chance to send us feedback through the survey after dismissing it.
Re the contact link, the contact us page seems clear enough now that I actually peeked at it. (The problem here isn't so much what the Guardian is doing than it is what others are doing. All too often, it's impossible to find any useful email or phone number, and taking a step to contact a company amounts to wasting your time. I can't remember the last time I bothered to look at any large company's contact us page.)
I haven't checked for other things but the same logic about protecting original licensed works should be borne in mind for any commissioned artwork, icon sets, widgets, third party items, fonts, etc.
An open-source version should go into the project (safe defaults that work), and the closed-source/licensed things should just be merged during deploy.
I only glanced for a few seconds, but custom icons and images are the other obvious areas of concern given it's your brand identity and you probably aren't open-sourcing that and have restrictions on how those assets are used.