If your one of the types of people that are amazed by how great a website can look by having it completely flashed-based you need to take a step back. Flash was not created to make websites into movies; websites are websites movies are movies. Have you ever wondered what the Google Bot thinks of your movie based website? The answer is plain and simple: nothing . Nothing by itself would not present a valid argument. To mention just a few:
1) Text within flash is NOT indexable – While this argument may be very obvious I can not tell you the countless times I have explained this to customers that a bot can not read text within a movie. When you create a flash file, it entirety it is a movie regardless of how you look at it.
2) Flash on a DSL line can take over a minute to load – If you are lucky, you have a total of less than 12 seconds to drag a customer in and keep them for good otherwise they are off and onto another part of the ocean (eg another website).
3) Navigation Effects with flash are not worth the hassle – How many times have you seen on a hover effect (when your mouse is over the link) the background just change colors? This can be done with xhtml and css and is a much more feasible solution.
4) Flash in place of graphics – People place graphics within flash, this type of development not only wastes file system space, but also defeats the purpose of marketing a website because it takes forever to load.
To wrap up, flash design is used in excess and should not be. I believe people who design sites primarily in flash do not know the harm they are doing to themselves or their clients from a optimization standpoint. Flash is not indexable and should be used sparingly (eg Photo Effects).