There's a 3rd party statistical tool available for free called SLStats over at SLBuzz.com. It works like that: you visit their in world store, get a sensor - one per avatar only is their policy. You need to get an account over there to make it work. Then you should place it at the main telehub of your place/sim and let it do its magic.
It's submitting the statistics on a regular base and you can take a look at your statistics then on a login protected webpage. A sample report is visible here. It looks quite good and reasonable, well, more like a logfile analyzer for a web server like Apache than the normal traffic counts. But, of course, the weakness of all such external solutions is - it has no impact on the in world search, if not all major sims are using it to report their traffic, it's still useful for the place/sim owner, but you cannot count really on the traffic comparison lists if there are major places still missing.
And, of course, there goes your data, and you don't know if they are going to begin to charge you in the future for this service or not. Still, a very interesting solution. But also, if it should use a range based avatar scan sensor, something that can add up to the lag of a sim.
In the right hands and used right this can be a valuable tool.