Animations to draw viewer attention can be developed with gifs, javascript or flash, but they should be used sparingly. The more frenetic the activity, the less likely it is that the image will enhance your message.

Constant jitter in the gif will draw focus away form the text. That said, there are instances when a well developed animation can speak volumes in a small space.

The 2004 image above says that games on mobile phones are fun, and hints that the game can play on many phones.

Animations can be used to set emotional tone, but are best used to illustrate actions, or link ideas that will be developed in the text.

Animated advertisements can entertain or annoy, depending on the wit behind the idea. Motion for the sake of motion is not enough. Animations should convey information, and the overall effect should not continue past the point when the viewer has tired of the image.