Compiled from the Note Identification Project thread:

Pink Grapefruit, unknown origin, Perfumers Apprentice - This is my daughter's favorite note. I have to admit, it adds a great deal of interest to perfumery. The bittersweet quality is remarkable. It smells realistic, like a thirst-quenching, cold glass of grapefruit juice. I'm not getting any of the off-notes that cause perfumers to turn to synthetics instead of natural grapefruit essence. Perhaps they occur when this substance is mixed with other ingredients.

Grapefruit - Nice, mild, tangy, bittersweet sample.

Grapefruit, Citrus paradisi EO (organic) from Frontier
I believe it is cold-pressed from the peel. What I smell is pretty much grapefruit skin, and it is quite nice. It is sour and bitter with a little bit of sweetness, same as you would expect if you were to peel a fresh grapefruit. Approximately 4 hours later: The grapefruit has mostly bitterness, as most of the sweet and sour has evaporated. This is probably where the perception of urine or BO comes from as it smells sort of "off". I can see why something else in the heart or base would have to take over at this point....