Most are not SuperchargersTesla's Supercharger network is getting most of the attention because it is quite innovative (more powerful than anything else, powered by clean energy, free-to-use for Tesla owners), but the majority of the growth in Tesla's charging infrastructure is actually coming from what the company calls "destination charging". These chargers are quite a bit slower than Superchargers - in fact, they're like the home chargers that you can install in your garage - but they're a lot less expensive and you don't always need the extra speed, so they're perfect for certain "destinations" like hotels, restaurants, and stores. Anywhere you are likely to be parked for a while, or overnight, is a good candidate.
According to Plugshare, Tesla added 858 charging stations across the US from September 2014 to September 2015. As you can see in the graph below, most of the growth comes from destination charging, which accounted for for a bit over 83% of the company's total chargers at the time.
This level of growth might almost seem excessive considering that Tesla doesn't make that many cars in the grand scheme of things, but this is obviously advance work for when the more affordable Model 3 EV rolls out in a few years. The plan is to sell hundreds of thousands of them, so having a ubiquitous charging infrastructure already ready to go will be a tremendous advantage, especially since Tesla's infrastructure is (still) proprietary while Teslas can, sometimes with adapters, plug into other charging stations.
The map above shows the "destination chargers" across the US and Canada.
And this one shows the Superchargers. As you can see, Superchargers are along well defined 'corridors' to allow long-distance travel, while destination chargers tend to be more evenly spread out wherever there is population density.