Niall Kennedy, widgetmaster of this parish, has written up what amounts to a guide to the sate of play with widget platforms in Universality of the web widget.
His conclusions:
A universal widget might lose out on advertising opportunities available in each widget platform's gallery. Your widget may not be listed in the Apple Dashboard gallery, the Google Gadgets directory, Windows Live Gadgets Gallery, etc. Users of each platform typically are directed to these directories to find new pieces of content and it's a free form of advertising for your widget and your brand.
He doesn't mention Clearspring or SpringWidgets here - though Clearspring may be a producing what will be the neutral widget platforms and SpringWidgets, although allied to MySpace, could also be looked at as a neutral widget platform. It's a very important issue. As Kennedy points out, using a platform that encompasses a widget destination can be seen as a limiting move. For example, if you build a Netvibes widget using their API, where does this leave you when you come to submit to Google Gadgets or a Yahoo environment? The answer isn't clear at this stage, but we can take a guess at what it might be. On the other hand, building and rebuilding widgets for every different platform or environment is a game that only the widget building agencies will want to be involved in. If you're being paid by the hour it may be attractive, but it's hardly efficient to have a dozen different flavours of your widget. And hardly 'universal' either. Maybe we'll see a genre of widget converters along the line of the Amnesty Generator, that will convert widgets to all the major platforms at the crank of a handle?
For the record, I would like to point out here that the term Universal Widget™ has been claimed as a Snipperoo Ltd trademark since the middle of last year.