The Good...
It looks great
It can be used to provide a rich animated interface
It can display text which looks much more effective than the ordinary HTML
It can be used to integrate sound

The Bad...
It is not readable by search engines.
It can't be navigatable by search engines
It can be slow at loading on telephone-line connections.

...And Our Verdict
Flash components add valuable impact to the user experience when integrated in the right context and this is largley dependent upon your business and the industry you are in.

Full flash sites are more suited to the media /arts arena where impact and a first impression is key and accessibility and compliance is not at the forefront when producing designs.

For the majority of sites we design, we would advise the use of smaller flash components such as animated banners to get key messages across. As opposed to printed material, users tend to scan through a webpage far more quickly and flash will catch the users eye more so than a key statement 'buried' in a long paragraph of text.