Premium membership is one of the filters LinkedIn lets recruiters use when they compile lists of prospects. It also lets you see how you stack up against the "skills" of other applicants for specific job postings (recruiters see this information as well).

Both of these make it easier to get your name and resume onto recruiters' screening lists. Can verify from experience that it noticeably increased both responses to my applications and cold calls from recruiters (although finding the right fit still winds up being a numbers game).