This talk was about non-relational databases. I didn't take a lot of notes :o) The most important morale is probably: don't keep the mind altering substances and the tools in the same shed.
With 2 decades of relational databases, they are pretty robust by now. They cover different spectrum of ACID compliance ; for instance MySQL is faster, Postgres is more reliable (though becoming faster... if you tick off the reliability options!). Relational databases are supposed to be normalised, except they are not really: there is also a spectrum here as databases tend to get denormalised for performance reasons.
Amazon uses an "eventually consistent" system, which they can pull off by charging at shipping time only. Conflicts are rare, if 2 orders are placed and there is only 1 item available, someone might get a gift certificate instead.
The NoSQL taxonomy includes wildly different tools that don't have much in common except for the fact that they don't use SQL: key-value stores, document stores, ....
CAP: Consistency, Availability, Partition tolerance. You can have 1 or 2, not all 3. (Brewer's Theorem)
There was only 1 Postgres database for all of SourceForge for a long time, while they were in the top 100 sites. Don't obsess about scale you'll never achieve.
One of the question was about how difficult it is to convert from a relational database to NoSQL. The answer is, from something like Postgres to MongoDB, it wouldn't be that much work (he did suggest 4 people 6 weeks though, which doesn't sound that trivial to me). Changing to Cassandra on the other hand would be a huge effort.