FileMaker has some great options for defining access to fields, scripts, layouts, etc at quite a detailed level. However, in my view, the current interface for setting those options is quite laborious to use if you actually want to go to the level of detail one should. As a result, developers either don't use these options at all, only set the major options - or spend more time setting things up in detail than would be necessary with better interface.
In addition to an overhaul of the current Security dialogues, I would also like to see options for setting the security options in the interface for the element you are working. The Script Workspace would allow you to set the access privileges for each script; there would be a similar tab in the field options, and so in.
I think this would make for a natural workflow for developers - you would set the security when working on an element, and not need to remember to go in to a completely different place once you're done and set the security options there.