I've had my Nook e-reader since November 2009, and my iPad since its April 2010 release, so let's round it out and say I've been reading e-books for a year. In addition to the Nook, and the Nook and Kindle apps on the iPad, I've got Nook and Kindle apps on my Droid phone, which are handy for pulling out a book when you're stuck somewhere.
In that time, I have read, to completion, around 14 e-books, mostly on the Nook. I haven't compared that to the number of non-work physical books I read in years past -- mainly because I usually don't keep track of such things. But my sense is that I am reading more now, in part because of the convenience: When I finish a book, I don't have to dig or shop for a new one; it's a couple of clicks away.
I've also switched from buying my family's books in physical format to buying them electronically. The tough part is getting them signed. Autographing electrons takes a very small pen . . . .