A flurry of stories and accusations have raised a lot of suspicion about vote counts, especially in Ohio and Florida in the 2004 presidential election.
However the total Ohio recount conducted in December of 2004 that effectively shifted the results by only a few hundred results based on allowing previously rejecte ballots suggests to me that the claims of counting conspiracies are probably misguided:
However I remain concerned by reports of defects in Diebold voting machines and optical scanner voting results that appeared to favor George Bush in 2004 by margins that are very hard to explain without invoking fraud.
Without a doubt our elections process is flawed so seriously that outcomes were certainly affected in the 2000 election where Gore would have won Florida without ballot errors, though I do not think this was due to conspiratorial activity unless you count the aggressive vote purging efforts of Katherine Harris and other Secretaries of state as a conspiracy. These suppression activities are probably legal in the narrow sense, though I think vote suppression efforts appear to have become a strategic part of many campaigns and this probably should be considered a somewhat nuanced violation of voting rights laws. Suppression efforts generally seem to hide behind the notion of preventing votes by felons and vote fraud, but I think that in general the true purpose is to alter outcomes in a partisan way.