Flash when used as a GUI was quite useful and produced good results.

But with the advances of web-based technologies I think flash is becoming less relevant and reduced to a cross-platform embedded video player. The only other "benefit" of flash is the embedded games people play in the browser.

My problem with flash is the engine is proprietory and the restrictive licensing.
Also flash does not degrade gracefully like html - no flash then access to site is usually denied.

With regards to Linux, flash is memory and processor hungry - I know it is supposed to be "optimized" with native graphics but it is still a resource hog.

Personally I hate flash and I think it has had its time.

However I think the haxe project is a nice idea and maybe has some potential.