The company Adobe, well-known for products such as Photoshop and Flash, has shown full support of the HTML5 specification in the past. Adobe also has a web development suite, Dreamweaver, in its arsenal of products, so there's a good reason for it to be supporting of future web technologies. Whilst there are the reasons for Adobe to support HTML5, there are also some which are the opposite – namely, the aforementioned Flash.
Flash, as you'll know, is the leader in providing Internet video and games, and is the technology that Steve Jobs aims to bring down a peg by essentially ignoring it on mobile devices. Jobs has been somewhat promoting lately HTML5 (a specification which can also provide easily embedded video) by apparently stating that it's the future of web video, and that Adobe is lazy with its Flash support, especially on the Mac. This is possibly worrying to Adobe, as Apple is a big player in the computing world, especially with the media market, so they would want to do what they can to keep Flash on top for as long as possible. In a private W3C mailing list, Adobe made an objection to the current specification being published, and has yet to make the objection public (despite promising to do so), according to Hixie's Natural Log. John Gruber of Daring Fireball noted that Adobe is attempting to block the API specification for the canvas element of HTML5 – an element which features 2D graphics, thus competing with Flash – as best as it can.
Larry Masinter of Adobe stated, "Do I need to repeat objections?", according to the minutes of a weekly phone status report. It will be interesting to see what comes of this, now that the objection is gaining attention, though hopefully it'll get cleared up soon.