In fact, looking through the site, the changes that make up Phusion 3 are incredible. If it works as advertised, there should be no advantages to running Unicorn or a pack of Mongrels anymore. I can hardly wait to try it out!
Some of us dont actually require the "ease of deployment" as performance is the priority, phusion passenger was never about performance as they've previously stated. While the new release is faster than their previous stable, it is still yet to be seen whether it out performs unicorn.
I'll reserve judgement until its been benchmarked against the other available deployment servers.
There exists a belief among some people that Unicorn is faster than Phusion Passenger 2. We've tested this a while ago and it turned out that they're evenly matched. Unicorn's speed is on par with Mongrel's. Unicorn's shared socket helps with fairly load balancing requests between processes but its positive effect on performance is not always significant. We've actually experimented with shared sockets and found that, when done improperly, it can actually hurt performance thanks to the thundering herd problem and the fact that catching EINTR in Ruby is expensive. All of Unicorn's I/O is handled in Ruby. A lot of Phusion Passenger's I/O is handled in C++. Instead we've opted to optimize our global queuing implementation to reach the same load balancing effect while speeding things up.
Phusion Passenger 3's speed surpasses Phusion Passenger 2 by far. You draw your own conclusions.
Of course you can take my answer with a grain of salt. I encourage you to verify these findings yourself.