Flickr may or may not be dead, but Google+ isn't going to replace it. The great thing about Flickr is the discovery. Flickr has a ton of tools that help you find other photographers (explore, tags, groups) and Google+ has none of these.
Whereas Flickr enables and encourages users to seek out new contacts, it seems to me that the purpose of Google+ is to better facilitate communication between existing contacts. He doesn't mention this in the post, but does anyone know how was the photo walk organized?
Exactly. Now, this isn't to say that Google couldn't create new solutions to some of these problems, but I get the sense that at its core, Google+ isn't going to be about discoverability per se, but about, as you say, connect with people you already know.
Flickr's search is actually quite robust and amazing. I frequently use the Creative Commons archives for my work as a writer. It's a fantastic resource.
Flickr might be dying, dead or stagnant, but I don't think that its replacement will be a slightly rehashed Picasa. Instead, I'm guessing it will be some sort of new network design that is able to surface photos from multiple sites and accounts and identities.
Whereas Flickr enables and encourages users to seek out new contacts, it seems to me that the purpose of Google+ is to better facilitate communication between existing contacts. He doesn't mention this in the post, but does anyone know how was the photo walk organized?