Open dictionary with command-control-d in Mac OS X

In a recent MacMost Newsletter, I came across the following handy trick in Mac OS X: while the cursor is over a word (not necessarily selected), one can press command-control-d to open dictionary which pops up a little window with the word's definition. This works in Safari and Mail, but not in Preview (unfortunately).

Previously, when I need to check the definition of a word, I right-click on it and then follow the link "Look Up in Dictionary". This will launch or pop up Dictionary with detailed information about the word (Dictionary/Thesaurus/wikipedia).

The right-click method seems to integrate better with other Mac OS X applications. For example, it works with Preview as well. However, now that I know it, I sometimes prefer the command-control-d approach better; it is quick and non-obstructive.