According to a message apparently sent from Apple's patent department, Apple is asserting patents over the “canvas” HTML element. This element was indeed invented over at Apple for their WebKit browser framework, at the time primarily for the benefit of the HTML-based “Dashboard Widgets”. The WHATWG has been attempting to document this as part of their Web Applications 1.0 (or “HTML5”) specification, and mostly-compatible alternative implementations of canvas exist in both Opera's and Mozilla's browsers.
I think this is pretty bad form on Apple's part. I've nothing against innovation in web technologies, but there's a right and a wrong way to go about it. The right way is to make an experimental implementation, and then if it's successful write down a specification so that everyone else can interoperate. The wrong way is to make your implementation, patent the hell out of it and then threaten and intimidate anyone who tries to work with your technology. Down that road lies a fragmented web that no-one wants to develop for.
This is particularly concerning having watched only yesterday a series of talks by representatives of Microsoft, Mozilla and Opera where all three pledged that they are no longer adding non-standard, proprietary “features” to their browsers, acknowledging that the web has only taken off as a platform in recent years because the platform has stablised and is, with a few notable exceptions, reasonably interoperable. An Apple representative was notably absent at this panel talk, because Apple refused to send anyone.
Microsoft did its fair share of this as well: DHTML behaviors, DirectX Filters, ActiveX embedding and probably more I can't think of right now. DirectX Filters and ActiveX embedding were basically dead on arrival as far as the rest of the browsers were concerned because they tie directly in to proprietary Microsoft technologies. DHTML behaviors were a nice idea, and the work-in-progress XBL2 is now heading towards a cleaner version of the same principle.