Amazon started offering some of its titles for free streaming to Amazon Prime users today.
For the record I use Netflix Watch Instantly alot via my Roku (which also supports Amazon Video On Demand) and I'm very familiar with Netflix's library. I'm also an Amazon Prime subscriber. If you look through Amazon's Instant Video selection list it's mostly a subset of the Netflix Watch Instantly library. If you come across titles unique to Amazon Instant Video i'd be interested in knowing.