For those not on FB, here is the text of Tim's post:
Quick update: We have some answers for why many of the stations are not sending data. It appears that many of the embedded device controllers don't behave very well with host names, and are sending data to us in a way that is not expected.
We love that enthusiasts building cool stuff send data to Weather Underground, so while we asses how to fix these issues, we have temporarily rolled back to our legacy system.
We will be testing over the next week to see how to fix these problems, and will ask for help from some of you.
I would like to personally apologize for this issue, we felt our testing was robust, but obviously there were gaps. We're still working on a plan and I will try to keep you updated here