Today I was working on a site migration from a proprietary CMS into Sharepoint for a client. Their existing site has a flash banner component which I thought would be easy to migrate - however, it turns out that when I package up the file in a module and deploy it as per normal to a Document Library (in this case, the Style Library), linking to the Flash component with <embed> no longer works.
It's not one of the blocked file extensions under Central Administration -> Security, the MIME type exists in the IIS website hosting the web application, and it's definitely not a permissions issue since if I place the link directly in the browser without logging in, I am prompted to download the file.
Looking at the Net console on Firebug, it seems like Sharepoint is treating the flash content as text, instead of 'application/x-shockwave-flash'. I eventually decided to get around this by deploying the .swf to the _layouts directory, but if anyone out there knows how to configure MIME types for a Sharepoint document library or have any other ideas as to why this is happening, please comment :)
As a random aside, I also needed to look into the contents of the Flash file, and came across Flare - a great little program to decompile flash files which gave me access to the original ActionScript. I don't know much Flash programming so I can't vouch for its accuracy, but it did the trick for me.