The current CVS tree contains support for the eventpoll mechanism used by Linux. You need a current kernel and a new glibc. With eventpoll, very fast event handling is now also possible on Linux.
The libevent sources in the CVS repository provide handling of signals via select() or kqueue(). Another change allows events to be persisitent when the EV_PERSIST flag is passed in with event_set. This takes better advantage of the kqueue() API.