1. Focus on a content region and click the Insert / edit embedded media icon on the TinyMCE toolbar.

2. With flash selected, you can add the following in the fields (for a Flickr slideshow):

General > Type > Flash
General > File/URL > http://www.flickr.com/apps/slideshow/show.swf?v=109615
General > Dimensions > 400 x 300
Advanced >  Flash options > Flashvars > offsite=true&lang=en-us&page_show_url=%2Fphotos%2Fgalt-museum%2Fshow%2Fwith%2F4112917355%2F&page_show_back_url=%2Fphotos%2Fgalt-museum%2Fwith%2F4112917355%2F&user_id=23686862@N03&jump_to=4112917355

 You'll notice it plays fine in the mini Preview window (I picked a public gallery of old b&w images from a museum they had showcased at the time).

3. Now click Insert, you will likely receive the familiar "F" placeholder.

4.  Save, Save & Publish, or view HTML

*POOF* ....Gone....

I wanted to spark up the conversation/concern. This behavior was discovered while trying to figure out what was thought to be a problem with my package: http://our.umbraco.org/projects/developer-tools/mysnippets-for-tinymce/bugs-requests/24701-Supported-Versions