It's totally inaccessible, and can only be seen by those with flash players. Quite a few mobile devices (for example, something called the iPhone), don't support flash. Hence, a totally flash website would be a blank screen. Not that useful.
It does seem to be supported though, just not quite as easily as a regular HTML + CSS + JavaScript site.
Hustle, I've just had a play around with flash and as far as I can see, you would not be able to use google analytics to track its impact. I'm probably too dim, but I can't see a way of inserting the tracker code successfully into a .swf page.