The process by which precious votes -- recorded on computer memory cards or cartridges, on optical scan ballots, or on traditional paper ballots --are translated to official election results holds the potential for errors. Generally, members of the public have a right to observe the counting process. If you're going to be an observer at polling places or tabulation centers tomorrow, or you're just interested in the process, please see these excellent videos prepared by Black Box Votingon how citizens can make sure that votes are counted accurately. If you don't think this can happen, remember the dozens of precincts in NYC that falsely reported ZERO votes for Obama.
A key general point: it is really important that results printouts produced at individual precincts be recorded and preserved (and copied or transcribed by observers when possible). When problems arise, having records of the vote-count at the local precinct (and individual machine) level is vital to untangling what went wrong, and correcting it.
This instructional video covers the system that will prevail throughout much of the country: transmission of results from individual DRE or optical scan machines to a tabulation center:
This one covers counting (often of absentee and other mail-in ballots) at a "central count facility":
And this film addresses Ye Olde counting and tabulation methodologies in use in New England:
And finally, a video on vote-counting under the Empire State's antiquated system:
Election officials are overwhelmingly conscientious, dedicated public servants who do important work under high-pressure conditions, and do their work well. But they can make mistakes, due to fatique, time pressure, and given the often error-prone machinery we use to record, store, and tabulate votes. Careful and painstaking observation of each step of the process from the time the voter leaves the booth until the final certification of the results by the Secretary of State or the state Election Board is important to make sure that "every vote counts" -- and is counted accurately.