Easy access to diacritical marks is often required when typing, especially when composing content in European languages and others that use them. On the Mac, the default method for accessing these marks with the US keyboard layout is to hold the "Option" key, followed by pressing a vowel that represents a specific accent character and then pressing the target letter's key; however, this may take time to get accustomed to. Therefore, for many US users the easiest way to use accents is to open the keyboard viewer pallet, and then press and hold the "Option" key to see available accent marks.
You can also use the character pallet to find obscure characters, symbols, and accents. The pallet is a little harder to use, especially for regular use, but it does have a "favorites" section to store commonly used characters for quick access. You can also search for characters, symbols, and components of characters, which can be useful for nonstandard uses of symbols.
These character and keyboard pallet windows float above all others, making them convenient for use in a variety of applications.
While these options are available in Mac OS X, the use of the "Option" key can be rather cumbersome for people who regularly use character accents. A recent tip over at "MacOSXHints" outlines an easier way to access accented character. According to the tip, selecting the "U.S. International - PC" keyboard layout instead of the default "U.S." or "U.S. Extended" as the computer's input source enables quick access to numerous accent marks. You now type either the Acute Accent (lowercase tilde key) key or the apostrophe key followed by a vowel and the correct character is used. Additional options are available by holding shift when using these keys.
On many systems, this is the default method for inputting accent characters and should be familiar to some people. For people more familiar with the Mac, this method removes single-stroke access to both quote and apostrophe characters, as well as to the acute accent and apostrophe keys which can be cumbersome to programmers.
To help overcome these drawbacks, if you enable the Input menu--in the Language & Text pane in System Preferences--you can add the keyboard and character viewers, as well as the "U.S. International - PC" keyboard layout to this menu for quick switching. This can be done by checking the box next to each respective input source in the "Language & Text" system preferences.
NOTE: If you already use an international keyboard layout, you will already have alternative methods for entering diacritic marks; however, these settings may still be useful for seeing what other options are available.