Flash is very good when used "properly". When producing forms or shopping cart applications, "good" use of Flash has provided a very stable base with which to perform credit card transactions and form submissions. Improper use of Flash includes badly compressed (or not needed) music, using 24-bit graphics when optimised 8-bit versions do the trick, and the inability to break down a process into small steps (this includes loading of media) so that stuff appears more quickly.
One nice example is on Interflora's UK website - their ordering process is essentially one page, using Flash MX.
Anybody wanna pay Macromedia a few thousand dollars for a RISC OS license?