Hey there - this is Seth from Google+. The launch partners will be rolling out Google+ Sign-In over the course of the day.
Fyi, the /apps link also doesn't work on my account.
It should shortly - the roll-out takes a few hours to get to 100%.
On an unrelated note, thanks for joining HN to participate in this discussion. It is really refreshing to know that Googlers like yourself and Matt Cutts are engaged in their community - it makes it much easier to have faith in the technology collaboration vs. when the movers/shakers sit behind a walled garden.
Hi Seth, since you're here, can you help explain how the Google+ OAuth relates to the GMail OAuth?
Are they just using different scopes and can you authenticate with both in one go or are they really separate APIs?
Hmm, looks like the blog post went up before the partners rolled out to their public-facing sites. None of the partners I spot checked have G+ login yet.