The 2.4 PTR is now officially up and as you would expect MMO Champion have all the patch notes.

Check it out. 

Why are people so worried about the 2.4 patch? Here a blue poster confirms that the notes will be released no earlier than when the PTR goes up.

We can't give an ETA other than that the notes will go up when the PTR does.

With regard to class changes... consider this patch "progressive". Well I would hate for it to be regressive!

I'm going to be a bit cautious in what I say in this regard. Will there be some changes to classes? Yes, there will be some. We're not rushing into a bunch of class changes for this patch at this point. Consider the patch to be a bit more progressive in nature. As we go along, the developers are going to be keeping a close eye on the results of any changes and additions and then making changes as they feel they are necessary. How many changes occur are going to be based on testing over time. This is why it's important for players to get in and test it as much as possible.

We want to make sure that the changes we are making are viable and practical for continued balance of the classes and don't want to put in too many changes at once and essentially skew the results too much one way or another. 

2.4 Patch notes are starting to come in slowly, here's a good summary from the people at MMO-Champion.

A good summation of everything we know about patch 2.4:

Patch 2.4.0 will be the second patch of 2008, and most likely the last one before the release of Wrath of the Lich King. The main feature is obviously the new Sunwell Isle and the two new dungeons, Magister's Terrace (5-man) and Sunwell Plateau (25-man).

• Sunwell Isle will be located off the coast, north of Silvermoon, and will be patched in with patch 2.4
• Sunwell Isle will be a major questing hub with a 5-man Normal and Heroic Instance (Magister's Terrace) and a 25-man raid (Sunwell Plateau). The goal with Sunwell Isle is to close the Burning Crusade storyline before the release of the next expansion.
• There are still a few scenarios left that could be released to provide the players with more content if WotLK gets delayed for any reason.
• At the release of the patch, players will access a small expedition camp where they can start questing.

Some big changes are coming to the way the UI is coded in patch 2.4, so they set up a proper thread in the forums to document them. Here's what's there so far:

Significant Changes
* The combat logging mechanism is completely overhauled with explicit data instead of text strings delivered to the UI. See slouken's post below for a sneak-peak at some of the current details. Highlights include detailed flags indicating relationship of involved units to player, unique identifiers for units with the same name within the combat log -- great for log analysis.

Visual Settings
* There's a new cVar unitHighlights; 0 = no model highlighting with Alt-Z, 1 = model highlighting on with Alt-Z. (e.g. /console unitHighlights 1)