Care for your absentee ballot...
Absentee voters should consider not sending their ballots back via postal mail.
First, you'll save a stamp. Second, lots can happen -- spoiling, subversion, misplacement, etc. -- to your ballot between when you place it in the mail and when it arrives at the Registrar of Voters. (If you do use postal mail, be sure to take it to a post office or, at a minimum, place it in a blue post office mailbox.)
The alternative is to seal and sign your ballot, keep it safe until November 8 and then take it in to any polling place (in Alameda county). This way, you won't have to wait in line at the polling place, you won't have to use the Diebold AccuVote-TS voting machines (which lack a paper trail) and you will have the peace of mind that the official record of your vote was cast on an indelible, physical medium (paper) instead of resident in (not-so-permanent) electronic memory and that you yourself were able to deposit it into a ballot box.
(In the longer term, Alameda County and San Francisco are moving to hybrid systems where most voters vote in the polling place using paper ballots and disabled and/or non-English voters use computerized systems with a paper trail.)