Here's the details, which have been added to the 4.1 patch notes on the official site:
02/04/2014 Leagues & Gameplay Update
Currently, the League system allows players to rapidly move up the ladder if they're playing at a high skill level. In some rare cases however, players were entering their promo series and facing off against unusually difficult opponents. We’re introducing a change that allows players to skip their promo series up to Platinum I if they continually play at a skill level a full tier higher than their current league placement.
- Players who consistently win against opponents a full tier higher than their current placement will automatically skip their promotion series as they progress to the next division. Series skipping will be possible up to Platinum I.
Bug fixesVision Wards
Vision Wards will now properly provide true sight to an enclosed area when placed in front (ie: dragon pit and Baron pit).
- Fixed a bug where Vision Wards weren't granting full true sight vision equal to their normal vision range
- Fixed an exploit with Blade of the Ruined King's active
Additionally, here's RiotSocrates with more information on the Promo Series skipping mentioned above:
The response to the start of the 2014 ranked season has been staggering. We are seeing more players involved in ranked play than ever before and though there has been a lot of positive feedback there has been a few concerns brought up about promotional games. Specifically, there is a concern that if a player does poorly in placements then goes on a winning tear they could get stuck in a promotional series against players who are more highly skilled than the tier they are trying to enter. We investigated how many players were actually in this position and it’s a very small group. That said this can be a pretty frustrating experience so we’re releasing a change to allow players to skip promotional series up to plat 1 in the rare case they are consistently playing way above their current placement. The number of players who will actually qualify for promo skipping is quite small since the vast majority of players are placed very close to their expected position. Also, it’s worth noting that the existing mechanisms for correcting fast moving players position will remain in play. So you can trigger this as well as division skipping at the same time.
We expect this change to go into effect sometime in the next 24 hours.