@macalter: I don't think so, if it works till now it should too. The "core" has not been changed. And of course we are talking about the flash mode only.
Could it be a user-end option as oppose to Admin making the choice? If the person can run Flash mode then let them have that option to see the slideshow in that mode. Akin to having html or flash options for pages.
The full size button was actually meant for the theme. I will see if that is possible, have to research flow players options (Btw, I don't really like sites with Flash/html options, to be honest I don't even like complete flash sites, too..:-))
@Jayray999: Tonights nightly will have separate width/height settings for the flow player in the slideshow and a note where to click for the full size mode below the player. I could not find any (easy) way to do that by default.