My office is completely paperless, and I send all client work and invoices via pdf.
in fact, I've started an e-series on my blog about going paperless (the series is called "Going Green") and you can read it / blog it / tweet it - the url is
http://julianeal.wordpress.com
I'm hoping to merge all the 6 blog posts into 1 to make a free e-book for your guide to start going paperless.