Michael Currie Schaffer makes a good point in The New Republic about the current wave of Republican vs. Democratic sex scandals. The Republican senators having sex with prostitutes or picking up guys in the men's room are sleazy. They deserve their humiliation, though, mostly because they are hypocrites. The Democratic mayors and governors who have extramarital affairs with other powerful people -- political aides, tv reporters, union officials -- are more dangerous because these affairs are more likely to lead to secret deals, payoffs, and conflicts of interest.
When two powerful people are married to one another, the public has some notice of the potential for conflicts of interest, and can keep an eye on them. In the case of elected officials, there are often legal safeguards against doing public business with the spouses of government officials. When the affairs are secret, though, the damage to the public can be hidden, too.
Extramarital affairs are sleazy any way you cut it. When both parties are power players, though, the sleaze is made worse by the corruption that is likely to follow.