real-time user presence polling or websockets tho

hey all, i'm thinking about adding a feature to show who's online and what pages people are looking at, you know, real-time user presence. my first ideas are either to have the clients ping the server every so often, or to use WebSockets for a constant connection. WebSockets are usually the way to go for real-time stuff, but polling might be easier to get going at first. what have you guys done for this kind of thing? when was polling good enough, and when did you absolutely need WebSockets? any problems with either method when things get big