Though I appreciate plurk mobile pages are served with content type application/xhtml+xml, some browsers cannot handle this content type properly and cause problems. Typically, Internet Explorer doesn't support this content type, and displays download dialog.
Surely this is for mobile users, but some mobile browsers also have troubles in handling application/xhtml+xml. For example, OpenWave browser (default browser of au, the Japan's second largest mobile phone network) can parse that content type, but it fails to recognize charset for Japanese when served with that content type, and causes 500 errors when post Japanese text (even worse, it sends Accept header that includes string 'application/xhtml+xml'. So simple RegEx based content negotiation doesn't work in this case).
Those problems are not present when content type is text/html. I'd suggest to use this (text/html) content type, instead of application/xhtml+xml, for mobile pages.
When opening 'edit profile' or 'edit account' pop-ups in Opera, half the screen is blank.
I upgraded to the latest version of Opera (9.5) today, but I still have the problem.
No problem in Firefox or Safari, but Opera is the most standards-compliant of the three.