What is Smarty and why should you care about it?
Smarty is a PHP Templating Engine. In short, it is what wires together (a) all the logic in the game's backend with (b) how the data from the backend gets presented in the browser. It's the glue that holds together every page on this site.
You probably don't have to care about it. The only reason I'm announcing this is because it's a major version upgrade with breaking changes. I've done my best to fix everything that it breaks before enabling it, but mistakes of course happen, especially with big changes like this.
Please be on the lookout for anything obscure this may have broken (if you do find something, either reply here or more preferably create a bug thread) and enjoy the perhaps small performance boost this upgrade results in (the main benefit of the upgrade has more to do with my use of it).