I first learn about it years ago during one of my herb classes. I ran into it again later when I learned about my high cholesterol levels. It was recommended for its Omega 3 content. It's also high in vitamins C and A.
The best part is that it shows up EVERYWHERE! I let it grow last year and this year I'm harvesting more than I can eat.
Look for a low lying plant with fleshy leaves along thick stems. It grows in any kind of soil, though it seems to be particularly fond of my garden soil, and it takes off near the end of June. The flowers are small, yellow blooms. Next time you see it, don't be so fast to yank it out, or at least save the plants you pull for your next salad!