Editor's note: I was off by an order of magnitude on the cost of this feature; thanks to Ian Littman for pointing this out. The below numbers are now correct to the best of my knowledge. Math is hard...
T3 instances launched yesterday, complete with a Jeff Barr blog post. One point that was mentioned that I suspect will sail past many folks is that by default t2/t3 "unlimited" will be enabled on these instances by default. This is in many ways a good thing-- if you'd otherwise run out of stored CPU credits, your instances will not be throttled; instead you'll be charged an extra five cents an hour per vCPU when this happens. This has two consequences of which you should take note. 1. This has the potential to surprise you on your bill if you're either running these things at scale, or are very budget conscious. Students eating ramen, I'm speaking to you here-- I remember those days! 2. Your instances won't mysteriously slam to a halt and begin performing like complete crap.
On balance I believe this to be the correct decision-- but it's a deviation from previous behavior, and it's something that you should be at least slightly aware of. Good luck, have fun, and don't shame other people for their budget constraints.