As I do a lot of work that involves stills I invariably use different resolutions depending on the use of the graphic.

In some cases I have used the full 2048 maximum in order to be able to do A Hi Res zoom in and out of an image. Or if I am projecting across multiple screens you need to push the limits to get the resolution for stills. For example I recently did a show where my screen width was 4 projectors with a 20% overlap giving a total width of 3484 pixels so I needed every bit of resolution I could get. The way I program it gets me around the time it takes to load images this size.
On other occasions I have saved the file at say 640 x 480 when I know I will never blow it up to full screen.

I have also used the Animation Codec to speed up load times but only ever to pull up individual frames never for playback.

Lately I have been using the PNG format for transparency as the file sizes are considerably smaller than PSD files.

Conversely with video playback I have blown up PAL 720 x 576 files to cover 3 screens and the result has been more than acceptable. All depends on what your content is. If it is the heavily detailed Company Logo with an animation it will look really crappy if you blow up a DV file. Photo Jpeg is much friendlier for this sort of thing.

On the other hand a moving background without too many hard edges will look fine.

I think with all these things it is horses for courses. The corporate world really cares about stunning logos and product shots whereas the entertainment world can be far more forgiving.

The beauty of the Catalyst is that you have all these options and the only compromise is really working within the constraints of the hardware. Only some experimentation will give you a definitive answer.

Cheers

Toby