Regardless of whether or not the outcomes of these elections so far would have changed, there is a lot of evidence of vote fraud. The fact that some people think it should be taken lightly is frightening, though I suspect it is mostly because they simply don't want the campaign labeled as conspiracy theorists.
Iowa - Ballots were tallied in a "secret location" because of a supposed threat from Occupy. It took a very long time to get the final results and 8 precincts ended up missing, and it is reported that many of those were college areas. Anybody with a brain realizes that the potential for vote fraud is huge here. Then of course there was the last-minute rule change that allowed voters to vote without ID's...for all we know, other campaigns could have been bussing people in, ala Obama.
NH - Dead people voting.
SC - Dead people voting. Electronic machines arriving without the zero tape, meaning they *could* have come preloaded with votes. People not being allowed to watch the tallies take place. Reports of inconsistencies in some counties where everyone knows everyone, made pacts to vote for Ron Paul with friends/churches/etc and had a clear majority, that went to other candidates once the electronic votes were tallied. Easily tampered with electronic voting machines.
Judging the effects of possible vote fraud is difficult, but to say that it isn't happening and there is no cause for alarm is disengenuous.