One of the raps on the Supreme Court nominee being considered this week, Elena Kagan, is that she has never been a judge, never tried a case, and never argued an appeal until just recently.
Off the top of my head, the last couple of Supreme Court justices who were not judges before they went on the Supreme Court were William Rehnquist and Virginia's own Lewis Powell, who were appointed by Nixon. Rehnquist was in the Justice Department after several years of private practice in Arizona, while Powell the former ABA president was with Hunton & Williams, as it is now known. I don't think that either of these two suffered from lack of influence on the Supreme Court on account of their lack of prior judicial experience.
The passing of Senator Robert Byrd from West Virginia reminds me that in his book, he claims that President Nixon considered him for the Supreme Court, before the "surprise" nominations of Rehnquist and Powell in 1971. Evidently having a lot of free time on his hands, Byrd graduated from law school in D.C. while he was a senator, but never took the bar examination. I'm almost certain that Elena Kagan is every bit as qualified as Robert Byrd was to be on the United States Supreme Court.