As the local Lancome Counter Manager. . . . Greekgrrl said it perfectly. There are creams out there that will help 'brighten' dark circles (Vitabolic Eye for one). This would work for both genetic and sleep deprived circles. Another trick is to put the concealer on OVER your foundation - but you need to make sure that the concealer matches the foundation VERY WELL or you will have the reverse raccoon effect (white circles). Lancome also has a waterproof concealer that will stay on better than most others on the market. I usually end up with the residual mascara and sleep deprived circles and the concealer (as well as my glasses) hide them well.
I am also VERY anxious to try out the new mascara Lancome is introducing next month called MagiCils. It is supposed to come off with just warm water (basically disolve in the water - no raccoon eyes, no damaged lashes, no eye make-up remover, etc). It also comes in some GREAT colours (fushia, black, turquoise, violet, and aubergine. . .).
Sarah