wow excellent support, an extension on the fly ;) I could have built this myself but I wondered if there were any preset template variables I didn't know of.
@Sander: You are welcome ;) One note here, to avoid issues with view cache you will need to disable view cache for your template and use {cache-blocks} if you will not do it this all your users will see only one IP, as long as you clear view cache.
{set-block scope=root variable=cache_ttl}0{/set-block}
{def $server_vars=ezservervars()}
{$server_vars['REMOTE_ADDR']}
{cache-block}
//rest of your tpl code
{/cache-block}
@John: Works fine here. Do you have any errors? Did you clear the cache? Have you tried this code in your template?