Riffing on: Avoiding the Uncanny Valley of User Interface
Inspired by: http://www.codinghorror.com/blog/archives/000869.html
Never has a truer word been spoken. Trying to shoehorn desktop application UI paradigms into a web based application never ends well. Just look at 'A qWikiOffice Desktop' for a shining example of all that is wrong with doing this. When loaded on a Mac, it's going to look horribly, horribly out of place thanks to using pseudo-Windows theming. When loaded on an XP box (or even a Vista box running a 'classic' theme) it's going to look horribly out of place. More importantly, the question is what does your application gain from looking like this?
The answer to the question above will almost certainly always be 'it looks good' or 'it's got lots of features'. A web application can look good without apeing that of a desktop application. It can look better.
Whilst I'm mentioning this, I have to say that my most loathed example of the UI Uncanny Valley has to be itunes. It uses the Mac look and feel on Windows and thus doesn't fit in at all. Bleurgh.