Ben Smith makes the very good point that immigration is one of the dogs that didn't bark in this election: it was expected to be one of the central issues, working to the Republicans' advantage, but instead has hardly featured. In part this is because other issues have made the headlines, but at least before the financial crisis struck McCain could have changed that with a concerted push for tough border control.
Three different factors probably contributed to his decision not to do so. First, he is not the most credible messenger for this position: he has long been on the other side of the issue, even sponsoring a liberal immigration reform bill which conservatives pilloried as offering amnesty to illegal aliens. Second, though he officially converted to the conservative position while seeking the Republican nomination, he rarely seems able to muster much passion for it, suggesting that his conversion was not truly sincere. Third, his strategists may have calculated that running hard against immigration risked driving Hispanics further into the Democratic camp.
If so, that looks like a tactical mistake - despite some early problems in the primaries, Barack Obama has done just fine locking up Hispanic support. McCain had a better chance of gaining support among the wide swathe of voters concerned about illegal immigration.
One of the other dogs that hasn't barked this time around is gay marriage. This was a big issue in 2004, helped by the fact that many states held referenda on constitutional amendments to ban it. It seems to command less attention right now, although that may be changed a decision the Connecticut Supreme Court made today granting same-sex couples marriage rights in that state.
And then of course there is Jeremiah Wright. His absence from the campaign is notable, given the recent focus on Obama's personal associations. Expect him to make an appearance soon.