Please keep in mind the July 7th deadline is to register online or update an existing registration. If you are NOT registered at this time you have until July 28th to register in person at either the King County Elections office in Renton or at the annex office at the County Courthouse downtown. Don't think you've missed out just because the first deadline passed.
I learned that if your ballot was mailed to you but returned for any reason, say you moved but didn't update your info., you need to get that registration updated.
@3 It's worth noting that moving is an explicitly stated reason to update your registration, and therefore does not necessarily "prove" your returned for any reason ballot assertion.
VOTE!
See: http://www.kingcounty.gov/elections.aspx