Personally, I'm quite happy about the move. I use Flex Builder to build pure AS3 Flash apps too, which always left me confused about the naming bias towards Flex.
I agree that Flex has a good reputation in the 'enterprisey' sector, where they always thought Flash was a load of rubbish; but we know that AS3 is much more credible, and Adobe should have tackled this head-on. Applications built on the Flex Framework should be credible in their own right, regardless of the naming of the development environment you built it in. Businesses unhappy with the renaming can continue to build Flex apps in Flex Builder 3 (just update the SWC), or build it in any tool of their choice, as the framework is open-source, so no need to buy.
Too many people confuse the Flex Framework with the Flex Builder IDE. I build Flash apps. I may use the Flex Framework, or I may use the core Flash API, but they're still Flash apps. This is why I don't think the Flex naming should have been used beyond the framework. M$ name their IDEs in a very generic way, that doesn't imply any single lanuage or platform... I think this is a good approach.
With Flash Builder, I guess Adobe felt this was as generalised as they were prepared to make the IDE naming. This doesn't necessarily fit with the naming approach of their other CS4 components. For example, Fireworks isn't called PNG32 Creator, and Premiere isn't called H.264 Editor - but the output of these two platforms isn't as proprietary as the SWF format. My feeling is Adobe want to use the Flash brand.
So in summary, is this a bad move? No. Does this threaten Flex development inside large organisations with a historic allergy to Flash? Not at all. If the architect throws his toys out of the pram because Adobe renamed the IDE to Flash Builder, and he doesn't want Flash appearing on his system diagram... Explain that he doesn't currently have Flex Builder on the chart, so no change will be necessary! He'll still be getting the same Flash applications built on the Flex Framework that he got before the rename; so maybe it's time he put some of the old-fashioned prejudices aside.
