One of the little things that annoy me in Mail is the data detectors. These are the little pieces of code that make dates, addresses and other bit of information click-able so you can insert them into iCal and other applications. The problem with data detectors is that they get in the way. I find them cumbersome, although they do help you can turn them off.
To turn them off, open Terminal and type the following:
defaults write com.apple.mail DisableDataDetectors YES
Quit and then restart Mail. Your data detectors should be gone.
If you want to start them again it is really simple, just type the following into Terminal once again and your detectors should be live again. You will need to restart Mail.
defaults write com.apple.mail DisableDataDetectors NO
A very simple command that once again, enables you to do something quite complex that would normally be hidden.