I have been on Twitter since July 2008.
During the last five years I have sent over 2,500 tweets. Assuming an average of 15 words per tweet that means I've written about 36,000 words. That is a small novel or a small thesis or a very long essay.
I've noticed over the years that I've gradually found it easier to write tweets though I see many others whose tweets appear effortless and whose tweet count is 10 times my own, for instance @flexnib's 36,000 tweets would equate to 540,000 words (and a large number of small dog photos).
Now that I am blogging I find that the long haul of trying to say something in 140 odd characters has been a good training ground for saying something in half a page, with a picture for padding. Twitter has helped me to actually get to the point and just say it.
The other aspect that Twitter has helped me with is authenticity. My understanding of being authentic is to share an appropriate amount of your real self. If you share too little then you are dull, monochrome and plastic. If you share too much then you can be just plain embarrassing. Twitter has helped me to find the middle ground that is comfortable for me but still authentic (I hope).
Hooray for Twitter.