The importance of tracking when paying for clicks really can’t be overstated. Without a very clear idea of which keywords are converting into cash, you’re really flying blind. By my own admission, I’ve been pretty lax in regards to keyword tracking until only recently.
I realize there are some handy scripts around that make this a fairly easy task, but if you can live without the built-in reports, keyword tracking is really quite easy to implement yourself with just an Excel spreadsheet and a small bit of PHP code.