Information Week has an article out on how the Flash/Flex recipe (along with a tweaked-out version of the Eclipse IDE) will prove a serious development platform that rivals Microsoft.
There is merit to what they’re saying. Flash is literally everywhere (arguably on more machines than Windows) and it is lightweight.
Longhorn is Microsoft’s answer to delivering rich applications over the Web. We’ll see if they deliver. Knowing Microsoft, it will be bloated – thus defeating the purpose of going thin/rich client anyway.
On the other hand, you’ve got the challenges of a merger (Adobe/Macromedia) and all the soap opera that often comes with that.