The VR camp did a good job of preventing a leak last time; I can hardly recall one, and if there was I doubt it was more than a week-and-half. The live tracks were what most on here were listening to. Then there was the MTV/VH1 stream about a week or two before release.
The new album will probably be leaked 2-3 weeks in advance.
There was a leak quite awhile before the release for Contraband... I remember a radio station in South America played 8-9 songs from the album and we were all able to download the songs that someone recorded off the radio. It was a fair bit before the CD I think... a month?