I have seen a number of posts, lamenting the death of Easter Eggs, which can pose a reliability and security risk.
In the course of developing Excel 95, several Excel developers from the charting feature team were caught up in the Doom craze, and each day they would be spend about two hours playing network Doom in company time. At some point, a few developers decided to build their own 3D engine after hours. After several weeks, they decided it was too hard and abandoned the effort; however, all was not lost, the engine survived and became an easter egg.
It was done with tacit management approval. (Oops, I am not supposed to say that! Don't tell anyone.) The reasoning I guess was: Better the Easter Egg you do know, than the Easter Egg you don't know. The Easter Egg also underwent scheduled testing to make sure it didn't affect Excel's operation. For example, the Easter egg will only trigger if no document has ever been opened or modified.
That Easter egg was a whopping 100K, back in the days when Windows 95's minimal configuration was 4MB and magazines regularly complained about bloated applications. You don't hear about bloated applications anymore, since hardware has long since far outstripped the needs of software, and Microsoft perfected the art of performance testing.
In Excel 97, the 3D Maze Easter egg was replaced with a flight simulator. See if you can find my name in there.
You can find out the keystrokes for both Excel 95 and 97's Easter Eggs, by googling "Excel Easter Eggs." Purely from memory, I believe the steps are as follows: Start Excel. Press F4. Enter X97:L97. Press Tab. Press Ctrl+Shift+ChartWizard button on the toolbar.
Before I left Microsoft, I was seriously tempted to leave my mark by planting my own Easter Egg in Excel, but I ultimately decided against it.