Close
An active user list would need to let any user hide, or it'll drive away people. I know I prefer to stay hidden on most sites and being forced to have my online status visible would be a turn-off.

It's a bit tricky, since it would need to differentiate types of activity: RSS/atom queries don't count; maybe post/index wouldn't, since many people--myself included--idly refresh the index occasionally while doing other things (which doesn't mean I'm actually "here")...