On-demand download of code that runs on your machine outside of web pages' usual sandbox.. I don't see how this is any better than ActiveX.

I think the idea is that it's not "page-oriented"; an ActiveX or Java app as you'd currently think of it is something that sits within the content frame and disappears when you navigate away from whatever page delivered it. This is more like the way Firefox extensions work now, changing the browser itself.

In that way, there won't really be "my site's BrowserPlus plugin" the way there were "my site's ActiveX/Java applet"; instead, there will just be a few well-known plugins that many different developers will start relying on, similar to adoption of a new HTML tag (e.g. <canvas>).

In fact, I imagine BrowserPlus could be a good delivery mechanism for these "HTML update patches", adding, for example, SVG support to IE on-demand.

Well, at the very least, its cross browser / cross platform.

Great, now people can make web pages that shut down my Mac!

Or signed Java. Click to grant privileges, and it can do anything a local app could do. Perhaps BrowserPlus will offer better browser integration, but that's an incremental improvement, not a 'game changer'.