For me, the blurb should be before the TOC (as they are in print books). We're talking short blurb here, back cover text, not an opus or forward.
I've seen some books put excerpts at the beginning of the book, but I can't see the point. Excerpts are also good at advertising/storefront points, before purchase, but don't need to be part of the book itself... after all, once you've got the book, you've got all of the text!
As a self-pub, I've not thought of putting a blurb into my ePubs (the blurb and excerpts are on my site, before purchase). I do include the blurbs of my other books at the end of the novel, as advertisement, but that's been about it.