There is a great summary of voting machine issues - The Landes Report.
And now my own analysis? The sheer volume of voters, candidates and elections makes a line-by-line discussion impossible, but there are those who have made such an effort. Click here for more details. I do remember reading about a small precinct in Ohio that delivered more votes to Bush than there were eligible voters. How about 3,893 extra Bush votes in a precinct with only 638 total voters? More details - along with a suggested cause - are available here.
So I cannot speak to every contest. I can give specific examples of things that concern me, though. I am concerned that the official overseeing the close results in Ohio in 2004 was the Secretary of State Ken Blackwell, who prior to the election had promised to "... deliver Ohio to the Republicans." And this is the same person who championed the Diebold machines for the state, while arranging $10k per plate Republican fundraisers at the home of... you got it... the CEO of Diebeld. Cirumstantial? Yes. Coincidence? Perhaps. Concerning? Definitely.
On November 2nd, HBO will premiere their new documentary Hacking Democracy. I'm sure I will have more to say after I watch it.