I keep comming across websites that have vital elements built in flash and no alternative content, its especially bad when the content is delivered in the latest version of flash, you will lose 5-10 percent of your visitors that way.
If your using flash it should be used sparingly, never for essential content and it should always have noflash content, especially for SEO.
And unless there is a necessity to use tha latest version of flash, you should always try to save for backwards compatibility.
Flash 6 if possible.
Scripts like UFO are ideal for something like this.
http://www.bobbyvandersluis.com/ufo/