It's true that the PlayBook also supports Adobe Flash, Adobe AIR, and Oracle Java, so apps for those client environments could run on the PlayBook -- assuming that their mouse-based interfaces can be well mapped to touch gestures. That's easier said than done, as Microsoft's disappointing Windows touch UI has shown. (And Apple's refusal to support them has had no discernible effect on its mobile devices' adoption, though that may be because most other devices don't support them either.)
You will also be able to use HTML5 apps on the PlayBook, but that's just matching what the iPad and coming Android slates can do. It's no reason to choose a PlayBook.
The security illusion
RIM is boasting that the PlayBook is enterprise- and CIO-ready. What does that mean? Just that it uses the same security and management tool (BlackBerry Enterprise Server) as the BlackBerry smartphones. That's to be expected -- and in fact required by IT. But the implication that the use of BES to make the PlayBook enterprise-ready somehow means the iPad is not enterprise-ready is a falsehood. The fact is, iOS 4's security and manageability capabilities are more than adequate for the vast majority of enterprises -- and they support the iPhone, iPod Touch, and iPad equally.
Security and manageability are no longer legitimate reasons (except in a few industries) to disallow iOS devices. RIM would like to pretend otherwise, but it's simply not true. However, it is legitimate to say that the Android OS is not able to meet basic enterprise security and manageability requirements.
Too small of a device?
The PlayBook will have a 7-inch widescreen display, so the unit is smaller than an iPad. I suspect that will make Web pages and videos feel cramped. Even on the iPad's 9.7-inch screen, many Web pages feel tight to me, given that most are now designed for 19-inch monitors. Ditto for business-oriented apps, such as presentation and editing tools -- especially when the onscreen keyboard is visible.
The 7-inch tablets I've seen have all felt awkwardly sized, and I'm hard-pressed to see how the PlayBook will not suffer the same squeeze.