A WebmasterWorld thread reported a bug with the AdWords Editor where the downloading and uploading of data was simply stalling out. Some of those receiving this error noticed error reports reading "Error Number 87," where one tries to pull down the changes and the "download in progress" dialog pops up, but it sticks at "retrieving changes".
These issues seem to be persistent issues from last month.
AdWordsAdvisor said the issue has now been isolated and should be resolved shortly.
Back with a brief update - the issue at work here has been pinpointed and looks to be on track to be fully resolved shortly.
I'd guess that most folks who were seeing this will now be good to go - while those who are still having an issue will find things resolved soon. I hesitate to name an exact time, though, as I do so hate to be wrong - especially in public. ;)
To those who were prevented from using AE today, my apology.
Forum discussion at WebmasterWorld.