Adobe brought transparency to the Illustrator world back with version 9. One of the many complaints about the poor-selling AI9 (and believe me, if you used it, you could see why nobody liked it after only 5 minutes of use!) was the inability of linked spot color EPS photos to interact with all the transparency features.
If you are designing an icon in Illustrator, select the Window/New Window menu to open a new view for the same document. Now select the View/Pixel Preview or press Apple-Alt-Y (Command-Option-Y) to change one window to pixel preview mode. Place the two windows side by side and enjoy seeing your logo in pixel preview while working on it in vectors. This way you can make sure you're using the right line width and see how your curves translate to pixels.
Today I'll tell you about a feature that's not really useful, but it shows that programmers at Adobe are fun people or have too much time on their hands. You decide.
Alt click the little triangle on the bottom left of your document to get a menu with some extra features. If anyone knows who is Ted let me know, because I've got his phone number. :) Which one is your favourite easter egg?