Firstly, congratulations to Adrian Chadd for starting the httperf port to libevent. Already we have seen some massive performance enhancements. CPU usage on my opensuse 11.0 workstation has improved about %3000 percent.
Certainly there is some stability work to be done. I am currently getting segmentation faults with very high request loads.
The current implementation does not use a persistent event loop, which means that the other useful features that libevent provides are not available (timers for example).
Something I want to see developed going forward is an asynchronous http client library around. The http work already done with libevent is certainly a start to this, but is far from complete. Essentially, what I want is a client api where I can perform some http client action asynchronously without needing to deal with any messy details.
The intention here is to foster a deal of code-reuse between http implementation projects that all use libevent at the core. After that, portability sits firmly on libevent's shoulders (where it belongs).