I used to use two tools at work. A web-based application called Seibel and Lotus Notes.

Seibel was the tracking program for pretty much everything. Notes was E-mail and knowledge management. Then we bought this other company. Then we started to use outlook. Then we started to use some in house tracking program which no longer integrated with our phones, so we had to install another application handle that. Most recently we started to use another program for knowledge management. Not to mention when we changed tracking programs some of our other tracking that was handled by Seibel stayed in Seibel and other parts went to another application.

From two tools for nearly everything. Two windows IE and Notes. Now we must launch at least 4 applications to get anything done.

Notes and Seibel had their quirks... But I'd rather use two highly functional applications rather than five, six or more that are semi-functional...