There's one point Glenn forgot to mention: GIF files support multiple "frames," which means they can be used for simple animation. I believe this feature is exclusive to GIF since, until Netscape supported it, no one had bothered with this rather obscure part of the GIF specification. PNG was designed before Netscape supported multi-frame GIFs, and the designers didn't see the point of supporting this completely unused feature. Pity.
Expand Finder Columns Quickly
Column view in the Finder is great for navigating through your disk's hierarchy, but the columns often aren't wide enough to show the full names of all the files. To expand a column to a width that will show all file names in their entirety, double-click the handle that you would normally drag to expand or shrink the column. To expand all the visible columns to that width, Option-double-click the handle.
Set up short abbreviations which expand to larger bits of text,
such as “Tx” for “TextExpander”. With the new custom keyboard,
you can expand abbreviations in any app, including Safari and