You don't need to know how to use Flash, nor even own it, to create slick .swf art for your web site complete with plug-in detection code. Just create your artwork in Illustrator, then go to File > Export and choose "Macromedia Flash (SWF)" from the Format drop-down menu.
The resulting Macromedia Flash (SWF) Options dialog box offers a ton of goodies, and the following tips are all found here.
To create a static piece of vector web art, choose Export As: AI file to SWF file. Since virtually everyone has the Flash plug-in already installed in their browser, they can see its fine, clean lines without problems.
Note that the "Create HTML Code" checkbox is enabled by default, so you'll get two files: the .swf file itself, and an .html file that contains the Flash plug-in detection code surrounding the reference to the .swf file, just in case someone doesn't have the plug-in. You could copy/paste this code into an existing web page if you want.
If you drew an animation key frame in each layer in the Illustrator file, you can make a Flash animation from that by choosing Export As: AI Layers (instead of AI File) to SWF File. Or if you *do* own Macromedia Flash, you could choose AI Layers to SWF Frames (instead of SWF File) and then edit the frames further in Flash.
New in Illy CS2, you can make a Flash animation out of an Illustrator blend without releasing the blend steps to individual layers first. Just turn on the Animate Blends checkbox, and choose either In Sequence or In Build.
This is actually really fun … use the Blend tool to create a blend from any shape to another, or even an instance of live text to another bit of live text. Zip over to Export as SWF, turn on the Animate Blends checkbox, and open the resulting HTML file in your browser. Woo-hoo! And it's so easy!
One key missing ingredient in Illustrator is the ability to set how long a selected frame (layer) should persist in a Flash animation. (Not surprising, since Flash really doesn't use this method to create animations.)
At the conference, Illustrator guru/pre-press expert Mordy Golding did an entire session on Flash and SVG in the Creative Suite. He showed how you could create multiple duplicates of an Illustrator layer to "force the frame to stay longer" in the final animation, which worked okay but required a bit of experimentation. Or, as I said above, you could just export the layers to Flash frames and modify their timing in Flash.