Just about as simple as it can get.  A generator item that displays safe area overlay guides for users working in 16:9 formats but who are creating for 4:3 or 14:9 broadcast.

All the obvious controls are there ...not especially pretty or perfect by any means, but what do you want for free! 

Not a priority, but obvious improvements waiting in the wings are to add freely adjustable guides, so that users can define and mark their own areas within the frame; add controls to turn on and off guides individually as well as by group; and also simple color picker controls so you can choose your own guide colors.

For now it works great as is, and is currently the cheapest option available.

UPDATED 21/03/08:

The new version (v2) shown adds in all modifications noted above : the freely adjustable user guides, the option to toggle on or off guides individually, choose your own guide colors, and fully mask cropped regions ...

UPDATED 14/10/09:

New version (3.1) adds some nice new options, including 16:9 guides, an EBU/BBC compliance override, full custom guide controls (so that you can set the guides to display according to your own specific numbers ... or those of a delivery spec), plus a “Conform to 16:9” option which you can use to force the guides to display within a center cut 16:9 frame if and when your sequence settings are not 16:9.