DDA stands for Disability Discrimination Act and in terms of Web development DDA compliance means creating fully accessible websites. As you know, search engines have problems deciphering flash, java and frames.
But DDA doesn’t refer to search engines. DDA refers to other tools: screen readers, hand operated devices, etc. It makes no sense to get into details now. You can read a comprehensible article on this topic here.
The purpose of this entry is to warn you on the drawbacks of flash websites. Flash is an interesting technology with enough pro features to make it recommendable for specific applications. Interactive CDs, entertainment sites or greetings use Flash because so far this is the best technology to serve their purpose. But business sites (unless you go for a interactive presentation of a product/service/company) should stay away from this technology.
SEO is almost impossible (relying solely on inbound links is passé). There is no chance of DDA compliance. This technology has many hidden costs: we are not talking only about expensive setups, we talk about broadband, loss of potential customers (believe it: Flash is annoying for many Web surfers). Flash slows down the time needed by a website visitor to find the information he/she needs.
To make a long story short: Search Engine Oracle is not against Flash sites in general. I just warn you that SEO costs for such websites are higher, the optimization more difficult and there are no warranties for good search engine results positioning. A really cool Flash design will probably get you enough inbound links from Flash fans, but are you going to be happy with high PageRanks when the revenue is close to zero? Think about it!