Mine updated with no apparent problems, no sign of a watermark though.
Almost 12 hours since upgraded. No issues so far!
RE: Announcing Windows 10 Insider Preview Build 10586 for PC - Page 14 - Windows 10 Forums
My Store issue was solved by adding DNS servers manually in IPv4 properties. Tested with Google's DNS servers, primary 126.96.36.199 and secondary 188.8.131.52, store started working normally. Setting DNS back to "obtain automatically" brought the issue back, Store could only be launched once per session.