Have you experimented with single page web application, i.e. where the browser only \'GETs\' one page form the server, the rest being handled by client side javascript code (one
The main reason to avoid it is that taken alone it's extremely search-unfriendly. That's fine for webapps like GMail that don't need to be publically searchable, but for your blogs and CMS-driven sites it would be a disaster.
You could of course create the simple HTML version and then progressive-enhance it, but making it work nicely in both versions at once could be a bunch of work.