We have about 150 taps into 100+ trees. I didn't count closely. This is actually a college club project that I mentor. It is sold, but at slightly inflated prices for fund raising. I just looked on Ebay and you can buy 1 gallon of Michigan maple syrup for $50 dollars per gallon delivered. That's quite a deal.
Other tree species can be tapped: most maple spp., birch, walnut,and few others. I have no experience with this. Sugar maple tends to run around 2% sugar and everything else is less, so even more work is required. Birch is finicky, but I heard that guys with reverse osmosis set-ups can do well with it.
Out east, they are marketing bottled maple sap in an effort to mimic the coconut water craze (IMO). It's sold as Vertical Water:
http://www.verticalwater.com/ . Maple root beer is a real treat and I've been known to mix a bit of the half boiled product with a bit of whiskey.
I just finished licking the remains of the pre-bottling filter bag....very heavy, almost molasses type taste. YUMMMMMMMMM
We also hard boiled a dozen eggs in the boiling sap for fun. Great with your favorite hot sauce (Franks for me). The young-uns always have to endure my "can't break a raw egg with your fingers" trick:
Not my video...use the flats of your fingers, not your tips!