Thanks for the reply, David
I also canvassed some friends by email. My healthiest food nutty friend says, "Wheatgrass juicing is apparently not an easy thing to do correctly. So I've heard. Wheatgrass needs to be pressed, not chopped. If you chop, as with a blender, or a typical juicer I've been told your body cannot metabolize it. I'm not an expert and I really don't know if this is true or not. I've personally used my juicer that has the correct device for this, but frankly I don't care for the taste enough to want to drink it on a regular basis. I haven't done it in a long time."

The idea of digestability keeps coming up! I would have thought that the little green shot would be like a spirulina sort of seaweedy thing. Something you'd find in Odwalla juices or Naked Superfood drinks. But apparently it is potent, not mild.
In his cookbook about cooking for Google, Charlie Ayers says, "Wheatgrass is great for cleansing the blood of toxins. It also contains strong digestive properties, making it a good choice for those with slow digestion or constipation. If taken before a meal, wheatgrass helps you digest your meal properly and move it along through your system. If taken after a meal, your body is more likely to absorb its nutritional values."
Charlie Ayers says that he was skeptical about wheatgrass shots but was convinced by one of the cooks working at Google to offer the shots "and it took off like crazy." He says, "I had one woman who did nothing but trim wheatgrass, grind it up, and pout it into shot glasses. We even had a little bell you could ring after you downed a shot. Drinking this thing that was good for you just became part of the culture and pretty soon we were grinding up 250 shots a day --20 flats of wheatgrass – and the bell was going off all the time."