All Pine, Fir, and Spruce are edible; but not all evergreens are edible, like Yew. As far as the needles go, use younger ones that are brighter in color if you can. New growth tips in spring are even better. Pine needles are full of vitamin C and vitamin A, 4-5 times the vitamin C of oranges and lemons. This helped to save early explorers from scurvy. Native Americans used tree parts for tonics and medicinal tea. Pine needles are said to soothe sore throats, cough, and lung congestion and help with cold and flu, among other things. White pine seems to be the preference. It's said that Monterey Pine has an orange citrus flavor. Soft pines like the White Pine and Pinyon are said to have a less harsh pitch flavor than the hard pines like the Ponderosa or Monterey.
This can be used as an alternative to the more expensive Balsamic Vinegar.
Update: I tried it after 4 weeks, and it was pretty strong.
I'd use less needles next time, maybe 1/3. :) I'm not a balsamic vinegar fan; but I think if you like that, you
might want to try this.