The move to the Nikon D800 last year definitely increased the rate of growth of my backup stream, as you can see in the table here summarizing backed-up photos from the last five years. This includes a few months of using a Nikon D70 (6 megapixels), about four years of the D700 (12 megapixels), and a few months of the D800 (32 megapixels).
I’m not a fan of more megapixels, but you have to go with more megapixels to get all the newest features that the major camera manufacturers have to offer. And those megapixels really add up. I suppose it’s worth noting the Jamie & Alice factor, too – since getting the dogs in 2010 I’ve definitely been taking more photos. But on a per-photo basis, the D800 can burn over 50 MB on a single photo, several times the maximum size of a D700 photo. I also do some videos with the D800 (which the D700 couldn’t do), and those add up, too.
Here’s a more detailed view, a monthly breakdown of the growth of my backup stream from 2008 to 2012: