There's a significant amount of chatter tonight about the Pro Tour: Dark Ascension Top 8, specifically the quarterfinal match between Paulo Vitor Damo da Rosa and Jelger Wiegersma. Here's the situation:
PV attacks with a Primeval Titan and a Thrun, the Last Troll. Jelger has 4 Spirit tokens from a Lingering Souls and 2 Drogskol Captains (1 tapped from attacking). PV also has a Kessig Wolf Run in play that can threaten quite a lot of extra damage. Jelger blocks thusly:
3 3/3 Spirit tokens on the Primeval Titan
A 3/3 Captain and a 3/3 token on the Thrun, apparently placed in that blocking order
Paulo pumps up his Thrun with Kessig Wolf Run (and also regenerates). They go to resolve combat damage and two things happen. First, PV tried to trample an extra point of damage over to Jelger with Thrun, claiming that the Captain dies first, so the token only absorbs 2 damage instead of 3. Of course, this isn't how combat damage works. Although you do line up the blockers and assign damage sequentially--you have to assign lethal damage to the first blocker in line before you can go on to to second--the damage happens all at once. That means you have to assign 3 to the Captain and 3 to the token.
While this is going on, there's some combat damage on the other "side" of the table to be assigned, Prime Time versus 3 3/3 tokens. Based on the way the board clears out, PV apparently assigns 2 damage to each token, which if legal would mean all three of them die when the Drogskol Captain (the first) hits the bin.
But that's not how damage works anymore, not since the M10 rules changes. You still have to assign all your damage in order with lethal damage to each creature in line. Primeval Titan's trample doesn't change this one bit. The only thing that could possible change this is deathtouch, which allows you to count even one point of damage as lethal for the purposes of moving along in the blocking order and/or assigning trample damage. Thus, if Primeval Titan somehow acquired deathtouch here, it could have assigned 1 damage to each Spirit token and 3 to Jelger.
I saw one person try to interpret the last line of rule 702.18b to allow for this type of deathtouch distribution just with a trampler, but that just isn't the case. The pertinent line is "The attacking creature’s controller need not assign lethal damage to all those blocking creatures but in that case can’t assign any damage to the player or planeswalker it’s attacking." This just means that you don't need to assign lethal damage to as many creatures as you can (unless you want to trample over).
For example, if the Primeval were blocked by a 3/3 and an Academy Rector (and put in that blocking order), you might not necessarily want the Rector to die because it could fetch out any number of scary things. In that case, you could assign all 6 damage to the 3/3. You don't need to assign lethal to both creatures, even though it is an option. If you want to trample, you do have to assign lethal to both and go 3-2-1.
Over two-and-a-half years after the M10 changes and we are still seeing people get this stuff wrong (not that getting things wrong is exclusive to the M10 rules). Even I missed this interaction when I was watching the match live, and it wasn't until a discussion afterward that I realized the error. Largely I suspect this is because of how rare it is to see multiple blockers assigned where you would want to assign damage in such a fashion so as not to kill anything until the follow up when a lord dies or you Pyroclasm. There's years upon years of damage being assigned one way, and even with the new rules, this type of interaction doesn't come up enough for it to become ingrained in our heads.
