Here's a little Sunday perspective for you website designers and bloggers..
As we enter the age of legacy migration (IE: Taking existing websites and making them cooler looking with Flash, Silverlight, etc.), it's interesting to note that some of the most successful pages on the Internet are 'just plain vanilla'.
The most obvious example is Google. While iGoogle is available, Google.com is probably the most simple page on the Net. (It's also interesting to note that the company has never adopted a slogan or 'tag line', leaving them open to whatever challenges may lie ahead).
Others? Craigslist (still growing), Twitter, Friendfeed (although I got lost and had to find my way out of the new 'rooms' :), TechMeMe, and numerous others.
So-called 'plain' sites are also almost always easier for search engines to index.
I really enjoy watching both. Some of the newer sites employing next generation rendering technology are literal works of art, and more often than not, much easier to navigate.
If you're thinking about a legacy migration and you have an awesome search engine position, there are ways you can do it without losing it. In general, at this juncture, you may want to think about starting a separate website (NOT with duplicate content but simply making it clear about what you're doing in your landing page). A 'blank piece of paper' and a fresh start employing all of the 'basics' of SEO is probably better for most, than migrating your existing site.
There's lots of new stuff out there from Adobe, Microsoft, and others. Even some pretty decent freeware and shareware. Download some trials and get 'into the curve'.
Legacy migration will be the next big thing (It already is for larger corporate websites). For SEO companies, it's the next boom .... and well worth studying.