PLEASE, PLEASE, stop giving up after an hour or a day and falling back to 8.1. Upgraded Lumia 640 to this build from 8.1, then did hard reset (there are issues with direct upgrade still). Then I had almost every issue mentioned so far. 24 hours later, almost anything server side was fixed; all my SMS came down, MMS settings fixed, Skype and SMS merged properly with all my contacts coming down, Social apps/integration fixed itself, motion data works, notifications only come once and on time, tones are setting to what I change them to, the list goes on and on. Yes I started with almost all the issues mentioned here, and tried to use the forum and this thread to fix them. Some worked, but most I decided to leave alone and viola they fixed themselves (probably server side or system maintenance). The only issue remaining is the update of system apps, but Gabe Aul has side they are going device by device to fix that still. Other than that this is faster, smoother, and more functional than my 8.1 install (this is opinion of course). Battery life also has lasted longer now that all the issues have aligned themselves.
I'm not telling everyone they are wrong, or that there still won't be issues, but I think time for the server side and system maintenance to clean itself up is due before we start jumping ship and claiming "Windows 10 mobile will never be ready!"
EDIT: I do still have 3rd party app issues. LinkedIn, Run+, Twitter seem to not work with my Hawaiian regional settings (work fine with US regular)! Seriously...this is 2015 get with the program, not everyone is English only American citizens from the west coast. Also the twitter app needs a seriously makeover to match desktop.