Excellent idea! Desktop based GUIs should move towards HTML/JS/CSS like platforms. I think the biggest advantage of something like this is the ability of desktop utilities to be cross-platform and integrate better with web based and other desktop applications. Adobe AIR is a move in this direction. Adobe received around 1M downloads of AIR within the first few weeks (But its still too 'flashy' for my tastes (would personally prefer something like this)).
