The rule of lenity use to exist in Oregon, and it was a good rule. It limited the reach and scope of various criminal statutes when we couldn't really tell from reading the statute or looking at legislative history what the legislature intended. That is, if there was some ambiguity about legislative intent, the rule of lenity would favor a more narrow interpretation. In my mind, I compared it to the rule that ambiguous terms in a contract are found against the party which drafted the contract; since the legislature writes the law, they bear the ultimate responsibility for clarity and precision, which so often our statutes lack.
When the legislature got rid of the rule of lenity, the result was to inadvertently (or perhaps advertently) encourage broadly written statutes that are invariably interpreted in the way most favorable to the state.
I say the legislature got rid of the rule of lenity, because that's what the Oregon Supreme Court says it did.
The "rule" was abrogated by the legislature when it adopted ORS 161.025(2), which directs courts to construe penal statutes "according to the fair import of their terms." See Bailey v. Lampert, 342 Ore. 321, 327, 153 P3d 95 (2007) (so holding).
The rule of lenity still exists in federal court, because there is a federal statute that supports the rule. Every now and then, I'll read a brief or a federal opinion that hints that the rule of lenity is rooted in the due process clause, but SCOTUS has never said so, because -- in light of the federal statute -- they've never had to.
Looks like that's going to change. Today, SCOTUS granted cert in ten cases, and here's the last of the ten:
Henderson v. United States 11-9307 The petition raises two questions: "(1) Whether a prior state disposition resulting in a one-year suspended sentence, which is not appealable or considered a 'conviction' under state law, is a 'prior conviction' that has 'become final' for purposes of the penalty enhancement provision of 21 U.S.C. § 851; and (2) whether the Due Process Clause requires the court to apply the rule of lenity in choosing between conflicting precedents with regard to the interpretation of a sentencing statute when the issue has never been decided by the en banc court of appeals and neither decision has been overruled."
Okay, the issue isn't exactly on point: the ideal question for SCOTUS would be, "did the state supreme court (any state supreme court) err in failing to apply the constitutionally-rooted rule of lenity?" But I'll take this one.
When SCOTUSblog puts up a page on Henderson, I'll post a link. For the time being, if you've got an ambiguous statute (and as I've said repeatedly, ambiguity favors the state), I urge you to argue that due process obligates the court to interpret the statute narrowly.