How many times have you written a document or drafted an email, read it through, thought it was ok, pressed the send button and then notice that you typed a word twice or made some other error that you missed? I have done this more than I like to be honest. Did you know that your Mac can proofread the text and read it back to you using the new high quality voices in OS X Lion. Now I use it all the time to check what I have written. Listening to Mac speech to text forces me to slow down and focus on what I am reading, which in turn allows me to understand more of what I am reading or correct mistakes that I otherwise would have missed.
To use it just right click your mouse to bring up a context sensitive drop down window and select Speech > Start Speaking.
By default Mac OS X lion uses the voice, Alex. If you want to try another voice click the Speech icon in the preference panel, and click on the system voice drop down. In the preference panel you can also change the speed of the speaking rate, as well as define a shortcut to activate the feature.