Pros
The people are fantastic - the recruitment process ensures you'll get excellent, technically skilled, challenging colleagues. The technology is brilliant - Amazon as a whole really leads with the standard of internal technology. Working in the Glasshouse means you're working on Amazon Instant Video, which is a very sexy (and interesting) product.
Cons
Your experience will vary massively depending on who manages you. Management standards are wildly inconsistent, and some of the most senior managers display surprisingly amateurish leadership skills. The culture is very bureaucratic - expect to deal in wordy narrative documents for everything from feature specs to promotion justification. The constant priority shifts mean teams don't actually deliver a lot. The operational support required means a lot of engineers spend a week every month getting woken up in the middle of the night on a regular basis.