Before having children, I used (and appreciated) my under eye concealer like I did all of my cosmetics ... just another tool in the ole' toolbox. Now that I have two small girls, and achieve approximately 2.5 hours of REM sleep a night, I rely on it like it's the air I breathe.
My favorite combo is the Bobbi Brown Corrector with the Bobbi Brown Creamy Concealer layered on top. On a good day, the Bobbi Brown Concealer Brush works just fine. On other days, not so much. I feel like anything less than a spackle knife will not provide enough correction or concealing! Some days, I determine that NO amount of product will do the job and throw on the darkest pair of sunglasses I own.
The other day, I used these products along with my other make up and went on up to the mall. As I entered Nordstrom, I spotted the make up artist that had sold me these products standing at the Bobbi Brown counter. I knew she'd remember me because we had shared a moment during the color matching process. Feeling all proud of myself, I walked past the counter and said "hey look, I'm using the under eye concealer" - I said it just like Oprah says "John Travoltaaaaaa". I was really feeling myself. No joke, the woman says back to me "use more-eeeeee" in her own Oprah voice. OUCH.