A few days after Kernel broke the news that there is no distinction in Cataclysm boss kills, he's implemented what he hopes will address the issue. The goal being that the progression lists can properly convey raid size-based progression, rather than everyone being lumped into a single list.
The implementation is very experimental, as Kernel explains, but the tier 11 (10) and tier 11 (25) lists are now functional. Just be careful how you raid if you're concerned with showing up in the proper list. If you go killing a boss on one format, it will not be possible right now for you to be reliably ranked on the other. So a 25-player kill as your first kill will rank you in the tier 11 (25) list, and a 10-player kill will rank you in the tier 11 (10) list.
The separated 10- and 25-man rankings have been reopened.
They are still experimental.
(Though it's possible to record a kill if there will be like 15 players without 10-man achievements)
- They are based on timestamps of achievement criteria in normal mode and timestamps of achievements in heroic mode.
- 25-man kills most likely will be considered as 10-man for some time because not all characters being updated in the armory. Requeue guild updating in several hours.
- If your first kill was 25-man, then you won't able to record next 10-man kill for 10-man rating (as there will be no new achievements in the armory).
- If 25-man raid consists of players that have killed the boss in 10-man, then 25-man kill won't be recorded as there will be no new achievements in the armory.
If your guild is dabbling in both formats, this is going to play havoc with your rankings, as you won't receive credit for some bosses in each list. An example being Ensidia's 25-player rankings, due to them first killing the Twilight Ascendant Council on 10-player difficulty. So again, take caution in how you raid in Cataclysm for now, assuming you're goals are to be on these progression rankings.
In related news, Kernel has also deployed a new feature for guilds who have registered on the website: you can now designate your guild's raid focus. This won't actually affect your display in the rankings, but it's a cursory way to discover what each guild's focus is (10 or 25, or both) while perusing the lists.