Last week, many users lost access to their Google Now Cards due to a weird bug. Google has fixed the issue over the weekend and many are now able to opt-in again to re-enable their device to get these cards.
It appears some of the users said the issue began fixing itself on Saturday, but Google's Nealem didn't confirm things were fixed until last night. Nealem said in the Google Web Search Help thread:
You should now be able to access your Now cards but you'll need to go through the opt-in again to re-enable the device. Don't worry, it's super quick!Here's the support article that will walk you through it.
Many now seem relieved that the Google Now cards they became dependent on, are now working again for them.
Forum discussion at Google Web Search Help.