I started peeking around some of the available plug-ins, dubbed "peppers", and found Doorbell. Doorbell flashes your Mint admin interface whenever someone accesses your site (green for new uniques, white for repeat visitors).
After installing the pepper, I realized that it's not accurately detecting new hits. After a few minutes of investigation, I come to realize that it has to do with Drupal's use of Apache's 'mod_expires', set by default in your .htaccess of any Drupal install.
No worries, all you'll need to do is exclude your 'lastvisit.txt' file from being cached, and you'll be all set. I was lazy, and simply set it to not cache any '.txt' files. This should do it for you: