What would be a good resource for an experienced programmer to learn Flash?
Consider a very seasoned programmer that doesn't require any teaching of programming concepts and that already programmed Javascript. Someone who never created a Flash file, or even know what Flex is. Someone who could probably learn ActionScript in a day but still needs to learn how to apply it.
I'd suggest picking up or downloading a pdf copy of Colin Moock's Essential Actionscript 3.
As a seasoned programmer you may find a lot of it is reinforcing the things you already know, however I think it's the best starting point for someone looking to get into Flash.
Just out of interest what other languages do you have experience using, it might help to gauge what area of Flash you're interested in, from Games to Flex - Flash covers a lot of stuff now.
I'm sure you know that O'Reilly Media do great programming books, the Actionscript 3.0 Cookbook is my bible! If you know what you need to do and just need to find the correct syntax to do it, this will be ideal for you.
http://oreilly.com/catalog/9780596526955
Cheers, Will