Flash normally get's used for awful brochureware (as lampooned in the excellent Skipintro.com) but I think it's best use is as a lightweight GUI for web applications and projects like elearning.
It provides a highly controlable lightweight enviroment that never breaks (providing your users have the plugin). I mainly use it on intranets/extranets as here you know your target audience & this is where more serious apps are hosted anyway.
If authored correctly Flash can be much more effective on a low bandwidth connection than HTML. On an elearning project the flash developer knocked up 30 minute modules that weighed less than 200k! The users on 56K can be interacting with the content as the rest streams down. The trouble is so much flash on the web is bloated gunk produced by graphic artists (with no usability knowledge) rather than GUI developers.
Macromedia is bang on track to make Flash a GUI standard with these changes, particularly as it seems one of the few things that works on different set top boxes, Mobiles, PDAs & Desktop OS's. They just need to make it more accessible for disabled users, what about a version of the player that interoperated with a speech browser?