I think it's a quite understandable choice, don't you? There's this ability in 10.5 to connect any view to a menu item, and I thought it would be kind of cool to do it this way

Well, I think this is one of those times when just because you can do something doesn't mean you should. I would ask what the checkbox gives you that the standard, and more sensible checkmark interface doesn't? (To wit: checkmark on Skitch.com by @dmoren

Yes, maybe you're right. Will reconsider... But I still think it's quite good. You don't have to leave the menu when toggling that button on/off as you would with the standard choice. But an iTunes symbol and that good old checkmark probably is the best solution. Glad you like the app anyway. I have been struggling hard to make this come to life since all this soft subtitle stuff is undocumented from Apple's side. But as Gollum would have said, "We wants it!".

I think it looks awesome Jörgen. Dont change it, you may well start a trend!

The problem is functional. Try this: click and hold on the action menu, then drag down. You can't select or deselect the checkbox without lifting the mouse button and then clicking again. Additionally, the entry doesn't highlight when you mouseover it. These two things make it distinct from every other item in the menu—it behaves completely differently. That's confusing, and it could easily be remedied by adopting the standard checkmark interface.  

OK it's fairly cool but I think it's a case of doing something the wrong way and having to be clever to compensate. The first item should be a standalone item in the toolbar since it bears no relationship to the other export possibilities. Then the menu can just be an Export As: menu, with the checkbox 'Add to iTunes after Export' in preferences or probably also on the toolbar, just to the right of the export menu. Currently it's unclear whether the checkbox functionality only applies after the last 3 options or after you choose any of those menu items. Is that reasonable?

David said it right. Honestly I can't understand Apple's (and everyone else's) heavy adoption of the Action button for just about anything. Actually it makes more sense, and indeed would be easier for the user, to place an "Export as" drop-down button. In that case, the checkbox inside de menu would be an excellent choice, as the user could have the "add to iTunes" option right in the moment of choosing the format. Great idea!
Btw, the "click and hold" thing dmoren mentioned is very obsolete as it demands a physical effort that's no longer necessary since just clicking does the job.

@Alvaro: It's not obsolete, because it's still a valid option. You can't control how your user is going to to interact with your program, so it doesn't make sense to use a UI widget that only works with one model of menu interaction. It's a needless complication when the standard checkmark interface accomplishes the same thing in a far more elegant fashion.

Hi all. I have changed the action menu in version 1.1 of iSubtitle. Have a look at this page and let me know what you think. http://www.bitfield.se/isubtitle/about_exporting.html