I give it a 5 for the documentation because of the PDF tutorial (CPAN doesn't show it, but it is included in the distribution.
It seems very stable and efficient, and even has its own top utility with NetServer::Portal !
I hope support for epoll and kqueue will be added in the future (I saw that epoll was added to the todo list in this version!).
I give it a 4 for the interface and the ease of use because I don't really like having to do $_->w->data all the time if I don't want to use closures to get my data (wouldn't it be possible to provide it as the second argument for Perl callbacks? this would not break backward compatibility).
An excellent, easy to use, stable and mature module for asynchronous, event driven programming. Simple programs written quickly. Successfully used in very large, long running distributed systems. Still lacking a port to Windows, unfortunately (but it is reported to run on Cygwin).