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The link above has all the information about 4.1 which is the first major patch for Cataclysm. It will feature class changes/balancing, 2 new 5 man Heroics, and possibly a Looking for Guild tool. 4.1 is still very early on the PTR, and lots more changes are coming. Nothing is confirmed or set in stone and is possible to be changed or canned. I'll go over 3 of the biggest changes I saw.
Zul'gurub returns as a 5 man Heroic dungeon:
Originally a 20-player dungeon released in patch 1.7, Zul'Gurub will once again open its gates, featuring updated lore, all-new encounters, achievements, and improved loot! Zul'Gurub is now a level-85 five-player Heroic difficulty dungeon. To provide a new tier above the current Cataclysm dungeons, players can expect to find epic-quality item level 353 loot. The minimum average item level to enter this Heroic dungeon is 346.
Zul'aman returns as a 5 man Heroic dungeon:
Ever a player favorite, the level-70 ten-player dungeon of Zul'Aman is being reintroduced as a level-85 Heroic five-player dungeon. Zul'Aman will join Zul'Gurub in a new Dungeon Finder tier of Heroic dungeons, providing epic-quality item level 353 loot. The minimum average item level to enter this Heroic dungeon is also 346. While Zul'Aman will be more of a throwback to the original dungeon featuring many of the same encounters, players can expect to find some updated gameplay mechanics, as well as new environment textures and lighting.
With the Zuls returning, you may be wondering about the unique mounts that were once contained therein. New versions of the rare raptor, tiger, and bear mounts will be available, while the old versions of these mounts will remain unique to those who already have them. We'll reveal more about how these updated mounts can be obtained in the future.
Possible Looking for Guild Tool / System
This to me is the most interesting change, but according to the blog, there is a very small mention of this in the patch notes, but nothing is available for testing.
* Work has begun on a new Looking for Guild system. Further details will be provided when we are ready for feedback.
So what do you guys think? It is still very early into 4.1 and the blog is very recent, no word if any new raids will be available (The Firelands). Paladins got some balancing, as well as Warriors most notably. All of the above is available to be tested on the PTR, lookup http://us.battle.net/wow/en/forum/1181024/ to find the PTR and how to test 4.1