We often deal with clients that are planning to "revamp" their sites with Flash, with SEO having already generated tremendous gains in their sales. The thing that we most dread to hear is that they've hired an experienced "Flash designer" that will be taking their websites to the "next level." Unfortunately, that "next level" is often the basement – at least in terms of SEO results.
The bottom line here is that a site built entirely in Flash still faces huge obstacles. While there have been recent moves from Google and Yahoo! to try to index the content from combined Flash/SEO sites, those moves have not yet, from my experience, translated into SEO results or success (at least when compared to html sites).
We should make a distinction here between embedded Flash and sites built entirely from Flash. For example, a site that contains Flash elements but still contains basic html elements will not overly suffer, as the Flash element (usually a movie in a box on the homepage or elsewhere) is externalized. A search engine spider will generally not try to parse through any files that have been externalized in the code – they will only index the code that is readily apparent on the source page.
However, from an SEO results perspective, there are still major issues with sites that are built entirely in Flash, and SEO is normally the first thing that suffers. First of all, the URL generally never changes no matter where people navigate on the site. As any decent SEO practitioner will tell you, every page of your site is a potential entry page for a search engine. With a site built in Flash, SEO suffers even more as you only have one potential entry page, which is the main URL. This cuts off dozens, hundreds, or thousands of potential pages that could otherwise be indexed in Google and Yahoo! (and all other engines). When your only potential entry page in the search engine listings is your home page, it is very difficult to target a wide assortment of keyphrases, potentially eliminating SEO results or rankings.
Content is another very large issue. Search engines rank pages based upon a number of criteria, but one of the most important to SEO results is the text that they can "understand" on individual pages. At present, search engines read primarily html text (although some also read text in the PDF format) – which means that if you decide that you want to use a rare and fancy font that must be displayed in graphic form (since the visitor may not have that particular font available on his or her computer while browsing), the engine will not read the text and therefore will not know what the page is about, which could harm SEO results. Naturally, this also includes any of the text included in Flash. While Yahoo! and Google have recently announced enhanced capabilities in reading content within Flash, I have not personally seen that translate into great SEO results for competitive keyphrases.
One other emerging aspect is that as search evolves, more and more people are looking for information while they are away from their computers. Many mobile devices are currently incapable of displaying Flash content, although recent moves by Adobe to make "Flash Lite" available may change this. However, it remains to be seen whether people that are seeking information on a mobile device will even want to navigate through Flash, especially if they can get the information that they seek from a fast-loading html page. In my opinion, lean html content will be at a premium when a company is trying to target a mobile audience.
Despite the difficulties, it is not the intent of this article to assert that Flash and SEO will always be incompatible – merely that it is the state of the current situation. You can find many differing opinions on mixing Flash and SEO on the internet, but the true test is to try to find a Flash site (that is to say, a site built entirely in Flash) that you admire and see if it ranks well in SEO results for 50+ competitive terms that are related to the specific business (in Google or Yahoo!). In my experience, such sites that combine Flash and SEO are nearly impossible to find. If anyone out there knows of one, please let me know.
Flash can be, and often is, used for great effect on the internet, in interactive kiosks, and in many other applications. I'm not from the "any Flash is bad" school, although I do think that many Flash practitioners tend to get a little carried away and often ignore basic usability issues. However, sites built entirely in Flash with SEO elements are still, again in my opinion, like oil and water – Flash and SEO are obviously individually useful, but they don't mix well. Until they do, I will continue to advise my clients not to build sites entirely out of Flash – or, at the very least, to have an alternate html option for search engine and user preference purposes. At the end of the day, many clients are surprised to find out how many visitors actually prefer "old school" html.