As I wrote yesterday, the outcome of the 2012 election is likely to set the future course of the Supreme Court for a decade or more. A second-term Obama will have the opportunity to turn the Court decisively to the left. But there's more to the judiciary than the Supreme Court. Most cases don't make it to the high court. As a result the lower federal courts, especially the appellate ("circuit") courts end up making much of the law that we live with.
There are 874 federal judgeships in total. So far, Obama has appointed 126 judges, but given a second term the number will no doubt be closer to W's total of 328 judges or even Clinton's 379 (good statistics at the US Courts website).
On inauguration day 2013, the next president will start out with 92 judicial vacancies to fill (assuming that nobody else gets confirmed between now and election day). This includes three, count 'em, three, vacancies on the all-important DC Circuit: the court that hears most appeals from the decisions of federal agencies and which is very often the warm-up bench for future SCOTUS justices. The ability to appoint three new judges to the DC Circuit will help determine whether the so-called "independent agencies" will continue to operate as a rogue fourth branch of government without judicial check.
Incidentally, the high number of judicial vacancies is not necessarily due to Republican "obstructionism" (contrary to the mainstream media), but is at least partly due to the administration's incompetence. As Ed Whelan of NRO Bench Memos has pointed out, Obama let two years go by without nominating anyone to the then-existing two open slots on the DC Circuit. And now there are three open slots. Moreover, there have been a "significant number" of Obama's potential judicial nominees who couldn't even get a thumbs-up from the strongly liberal American Bar Association. But given four more years, Obama will eventually get his way.