For the last few years there has been an ongoing debate on whether it really makes sense to develop websites entirely in Flash. On one hand you have very creative designers who complain that the visual limitations of HTML give them no other option, and on the other hand you have the purists who complain that given the usability limitations of flash, it isn't really an option at all.
For movement and overall "cool" factor, flash really can't be beat. It allows you create very visually captivating animations and interactive applications that otherwise would not be possible inside a user's browser. This makes for great intro animations, fancy website widgets, and an increasingly popular method of delivering streaming video and audio. Flash is absolutely unbeatable at what it does well, the problem becomes when people try to develop entire sites using it.
In a nutshell, flash can generate great components of a site, but was never designed to be the framework to build your entire site with.
Problem #1 Bookmarking - Ever find a great page you want to send to a friend, or save to your book marks? On a normal HTML website, the URL changes on each page so you can send the link to your friend, or have your browser save it to your book marks. With a flash site this generally isn't possible. You'll usually notice that as you click links in an all flash site your URL stays exactly the same. That means there is no way to send people directly to a specific page.
If you visit this flash template, you will see as you click on the links, the URL does not change.
Problem #2 Search Engines - Search engines these days are very smart. When search engines look at your website they have been programmed to recognize normal HTML tags and give additional value to specific tags. For example if something in your HTML code has been designated as a heading, then the search engine knows that text is more important then text that just appears in a paragraph. When your entire site is in Flash the search engine often can no longer contextualize what is important and what is not, and in that sense you end up loosing ranking with the search engine. Many search engines like Google are now also begining to take into account what other websites link to you. Since you can't link directly to a specific section on your website if its all flash (see above) even if you have really great content people probably won't link to your site.
Problem #3 Accessibility - As the generation that grew up with computers continues to get older, and as more and more people in general are online, the number of people with disabilities using the internet is sky rocketing. Simple things such as color blindness or other visual impairements can greatly effect someones ability to navigate the web. Fortunately properly designed websites allow users to take advantage of special settings in their web browser to display information in such a way that it is easier for them to read and use - they completely control how they want sites to appear. Flash however doesn't recognize these settings, which for many users results in an unpleasant, if not downright useless experience. This can not only drive away potential visitors, but in some cases may constitute may actually constitute discrimination and is illegal.
We could go on about a variety of other downsides to flash only sites, such as download speed, users being required to have a plugin to view your site, maintenance costs.... but we don't want to beat up flash. It is an amazing tool at what it does, the key is just to use it properly.
So why would anyone use all flash for a website? The short answer is that with very few exceptions, they shouldn't. Usually people trying to sell you an all flash website aren't looking at the bigger picture. Normally its nothing malicious, they simply either don't know any better, or flash is the only tool that they are familiar with. On the more malicious side some companies have realized that regardless of the drawbacks, it is a lot easier to toss together a site in flash then it is to take a layout and properly convert it to standards compliant cross browser friendly css.
This is always a hotly debated topic and we welcome your comments. Let us know what you think, is an all flash website ever appropriate?