One new element in Icecrown Citadel are exponential soft enrages. These are mechanics which start out slow and "speed up" as time goes on. There are currently three fights that use exponential soft enrages: Deathbringer Saurfang; Professor Putricide; and Blood Queen Lana'thel.
In the Deathbringer encounter, Saurfang gains Blood Points when he deals damage to someone. When he reaches 100 Blood Points, he puts a Mark on someone and deals damage to them whenever he hits the tank. That means he generates the next Mark faster, and so on. If a person with a Mark dies, Saurfang heals for 5%.
In Putricide Phase 3, the tank gets a debuff which causes raidwide damage. Each stack increases the raidwide damage by a factor of 3. If the debuff expires for any reason, including tank death, Putricide is healed for a large amount (10% maybe, but P3 starts at 35%, so it's effectively a third or more of his remaining health.)
In Blood Queen Lana'thel, one person is turned into a vampire allowing them to do more damage. After a short time, they have to bite someone else and turn them into a vampire as well. After another interval, two new vampires have to be created, and so on. If you aren't able to bite someone, you get Mind Controlled.
One of the most interesting things about these setups is how vulnerable they are to "fiddling" in the early part of the sequence.
For example, in Deathbringer Saurfang, you can let the first Mark die. Saurfang heals for 5% and you lose a DPS, but you effectively reset the soft enrage timer. Let's say the first Mark comes at 2 min with the second Mark coming at 3 min. Letting the first Mark die means that the first active Mark comes at 4 min, with the second mark at 5 min. You gain a huge amount of time because you were able to reset the sequence, and the fight becomes trivial. The penalty of 5% health and a DPS is not enough to prevent the tactic from working.
In Putricide, the penalty is very high. It's high enough to make resetting the stack non-viable. However, you can buy a bit of extra time by inserting more tanks into the tank rotation. Each extra tank would give you an extra 40s in P3 while keeping the raidwide damage low. It's possible that a guild which is having trouble with P3 could drop a healer and put in an extra tank.
For Blood Queen Lana'thel, originally the sequence of 1-2-4-8-16 was less than the hard enrage timer. So people started doing a sequence like 1-2-(4-3)-6-12-24. When you hit four vampires, one vamp would deliberately die to shift the sequence slightly. A small change early in the sequence netted more time, enough that the hard enrage became the limiter. Again, there was no penalty for fiddling with the sequence. Blizzard eventually increased the timer, so the normal sequence would hit the hard enrage timer as well.
So exponential soft enrage timers are a very interesting mechanic introduced in Icecrown. However, they need strong penalties to avoid people tampering with them. An early reset or delay can push back the soft enrage by a large amount. In two of the three fights that use it so far, the penalty wasn't strong enough.