I usually use TextEdit for writing my NaNoWriMo novel. There's no easy way to get a word count from an RTF file without exporting it as plain text and running "wc -w" on it. And, it was an excuse to learn some AppleScript.
So, I wrote the following little script to count the words in the front-most TextEdit window. Yay geekery!
on run
set number_of_words to 0
tell application "TextEdit"
set number_of_words to count of words in text of document of front window
end tell
display dialog "The number of words is: " & number_of_words
return the number_of_words
end run