Hm, I think, that prompt should give you some hint of the environment and context in which the command you are typing will run. Username, working path, machine hostname, at least, of course (well, it isn't really necessary to show hostname, if you never use more than one machine, and so on). On the other hand, I don't like stuff like current time, number of running processes or system load, because they are not part of that context. They are constantly changing, and not only by actions and commands in the shell; when you are done typing and press enter, they won't be valid.
