I decided to do a DVD because I wanted to include a lot of screencasts. The companion PDF is more of a checklist/workbook. We did a 1,000 DVD run at DiskMakers and also let people access it online.
We're pretty much sold out of the initial run of DVDs (I have a few left in my closet) and we've sold the online version to a lot of overseas photographers who didn't want to wait for it to ship. We charged $79 for the DVD so you can do the math there. http://www.photographyseo.com.
One thing I want to emphasize is that we did absolutely no marketing other than linking to it on our main website and blog. No AdWords or other online campaigns. If I had tried hard, I imagine we could have sold 2 or 3 times the amount we have by now.
I'm considering doing a revised version that is an online/ebook version only–or possibly doing a version that has a slightly broader audience ("SEO for wedding vendors" for example).
If anyone wants to see the PDF or browse the videos, drop me an email.