I believe there is normally a thread devoted to the intermittent One Piece manga release that's typical around this time of year, but I haven't seen one, so I thought I'd take the initiative to put one together. We also posted an article on this with some more detail. All dates are for the official English/Japanese Weekly Shonen Jump release.
December 7th: WSJ Issue #1 - One Piece Chapter 809
December 14th: WSJ Issue #2 - No One Piece Chapter
December 21st: WSJ Issue #3-4 - One Piece Chapter 810
December 28th: No Weekly Shonen Jump or One Piece January 4th: WSJ Issue #5-6 - One Piece Chapter 811
January 11th: No Weekly Shonen Jump or One Piece January 18th: WSJ Issue #7 - One Piece Chapter 812
After Chapter 812, things should return to normal. For those looking for the unofficial scanlated releases there has been a recent crackdown on those illegally obtaining and posting the manga, so you may have to wait longer than you're used to.
Hope all this information helps. For those looking for things to do/listen to during these breaks, our podcast will have Greg's report from Jump Festa in the coming weeks!