The rules at Ignite are very simple but very strict:
The idea is simple: presenters are required to stick to a rigid format of 20 slides, each of which changes automatically after 15 seconds, ensuring that each presentation is exactly 5 minutes long.
They add "the format forces presenters to think long and hard about every slide", although possibly I missed that bit when I first signed up.
There were a few bits where I got flustered and said things which didn't make sense (I got left and right confused at one point). The bit about Adam Smith was garbled gibberish, as was the Twirls In Unexpected Places bit. I wasn't expecting people to whoop and cheer at pictures of maps and graphs. It put me off.
Apart from that, it was enormous fun and I recommend you take the time to watch all of the other videos too (I particularly recommend this look at British sea forts, and this analysis of the role Daves have played in history).