Johnson v. United States, Supreme Court of the United States, April 4, 2005 [ruling that where a prisoner challenges a federal sentence on the grounds that a state conviction used to enhance it was vacated, the one-year filing deadline for habeas under 28 U.S.C. 2255 begins to run where the prisoner receives notice that the prior conviction has been vacated]. Excerpt from the Opinion by Justice Souter:

Although Johnson knew that his conviction subjected him to the career offender enhancement, he failed to attack the predicate for enhancement by filing his state habeas petition until February 1998, more than three years after entry of judgment in the federal case. Indeed, even if we moved the burden of diligence ahead to the date of finality of the federal conviction or to AEDPA's effective date two days later, Johnson would still have delayed unreasonably, having waited over 21 months. Johnson has offered no explanation for this delay, beyond observing that he was acting pro se and lacked the sophistication to understand the procedures. But we have never accepted pro se representation alone or procedural ignorance as an excuse for prolonged inattention when a statute's clear policy calls for promptness, and on this record we think Johnson fell far short of reasonable diligence in challeng­ing the state conviction. Since there is every reason to believe that prompt action would have produced a state vacatur order well over a year before he filed his §2255petition, the fourth paragraph of the §2255 limitation period is unavailable, and Johnson does not suggest that his motion was timely under any other provision.

Read the full text of the opinion here [PDF]. Reported in JURIST's Paper Chase here.