Location-based bookmarking has been around for a while, but Flagr makes it really straightforward. The service allows you to send a text or picture message with your location and plot it on a Google Map. You can also explore bookmarks from other users. From the site:
Whether exploring new places or revisiting their favorite venues, most everyone you know is constantly exploring. Every now and again, you may hear of the travels, but more often than not, such news is lost to the hustle and bustle of everyday life. Flagr changes all this by enabling you to easily keep tabs with your friends’ most current whereabouts as well as their thoughts along the way. Whether it’s a killer burrito place or a new hilarious movie that your friends stumble upon, you are “in the know”.