NOT using Flash technology on your web site. It's very nice looking, but provides minimal functionality and value to most sites. Often times the navigation of Flash based sites is very clumsy. Updating ActionScript and Flash is extrememly slow and will result in a higher bill from your web developers. Most mobile devices still do not support Flash. More and more are supporting Flash, but it's been a very slow process.
If you will be selling anything on your site, Flash is NOT the technology to use for your store. We have yet to see anyone produce a good, large, high volume web store using Flash. Sure it can be done, but no one has put in the time, effort, and money to do it. That's because it will take a LOT of time, a HUGE amount of effort, and a FAT wallet! These factors are just toacceptance build and maintain a Flash based store and the ROI just makes that type of project an insane choice!
When to Flash ... If you need instant download/upload capabilities, Flash may be the way to go. Streaming vidwo and audio, at the moment, still work very well with Flash. Maybe HTML5 can grab some of the marketshare for streaming audio and video, but HTML5 is not ready for prime time and is only supported by the latest and greatest browsers.