I had never even seen a plumcot -- but based on it's name, and where I found it (right with the plums & apricots at Wegman's) it's not hard to figure out what it is. In the spirit of trying new things, I had to get one. Good decision! I just ate it, and it was quite tasty.... It had a sweet fruity taste, but it was not an overpowering or overly sweet fruit. I definitely recommend trying it (and I'm not even a big fan of apricots!)
In doing some looking around online, I found out that this is a hybrid that an American horticulturist came up with. It can be used in cooking just like a plum (I may have to try that sometime).
They are sized more like the plum, and priced like the plum - which is good since Apricots are significantly more expensive. It is supposed to be equal parts apricot and plum. They are relatively low in calories (one has only about 40 calories) - and they have age fighting antioxidants as well as immune boosting properties.
If you see it in the grocery store, I definitely recommend checking it out!