O'Connor's behavior in Bush v. Gore was unconscionable. The consequences of her vote in that decision outweigh everything else of positive import she may have done from the bench.
To clear up some misconceptions about "who really won", here's an extended passage from Jeffrey Toobin's "Too Close To Call: The 36-Day Battle to Decide the 2000 Election":
[quote]A joint study of some 64,000 ballots by USA Today, The Miami Herald, and the Knight Ridder newspapers sought, initially, to answer the first question: What if there had been no stay? This study examined only undervotes; it did not include the ballots in the seven counties that had completed their manual recounts by the time the Supreme Court entered its stay or those precincts in Miami that were recounted before the local canvassing board decided to stop all counts. Under three of four scenarios, Bush won this recount. If the standard for counting ballots was lenient—that is, dimples allowed—Bush won by 1,665. If the standard was similar to that applied in Palm Beach, Bush won by 884. If two corners had to be detached, Bush won by 363. Only by a strict standard—fully detached chads required—did Gore win, and by a total of only 3 votes.
[quote]At first glance, these results are curious: The Gore forces were always fighting for a lenient standard, and it now seems that Bush would have prevailed under such a rule. But this apparent anomaly can be explained by examining the counties that were not included in the study, which were the most Democratic areas in the state—all of Broward and Palm Beach as well as the northern part of Miami-Dade. If these areas were included—that is, if the undervotes in all sixty-seven counties were examined—then the race shifted in Gore’s direction.
[quote]A later USA Today, Miami Herald, and Knight Ridder review of 176,000 ballots, including 111,000 overvotes (mostly from optical-scan machines) helps to answer the second question: What if there had been a true statewide recount? Here, Gore did better. Under the lenient standard for a statewide recount, Gore won by 393 votes; under a Palm Beach approach, Gore won by 299; under a two-corner rule, Bush was the winner by 352; under the strict test, Bush won by 97. In other words, when the recount included the seven-plus mostly Democratic counties, Gore won under two of the four standards.