Sounds like something out of a sci-fi movie, but this is done commonly now with certain nutrients. B12 most commonly. There's some buzz about intravenous magnesium sulfate injections as well to increase serum magnesium.
However, now people are able to get a full spectrum of vitamins and minerals into their bloodstream at once. Part of me thinks this is a bit too wild to be used, but in reality it could be considered safe because of the few side-effects of simply having a higher level of certain nutrients in the blood. As long as someone has functional kidneys, it sounds like it's not a high risk medical procedure.
Although it's routine sometimes to receive IV doses of certain nutrients, it's not common for us to simply go in for a nutritional boost in "that way." It might be a good alternative to taking supplements, especially if it's shown to have significant enough benefits.
IV Magnesium sulfate Intravenous magnesium as an adjuvant in acute bronchospasm: a meta-analysis. http://www.ncbi.nlm.nih.gov/pubmed/10969219
My answer is the kombucha, lacto-fermented veggies, kefir, and other fermented foods rich in probiotics and lactic acid and lactic acid bacteria and other goodies and other good guys will heal one's gut so well that such radical measures are completely unnecessary. Absorption is the issue.
And intravenous vitamin therapy is not even close to paleo. And since my first paragraph solves the problem harmoniously and naturally (read: paleo-ly), intravenous vitamin therapy is probably unnecessary and unnecessarily expensive.
B12 injections are usually given to strict vegans who don't eat vitamin-fortified foods. Raw vegans are particularly susceptible to B12 deficiency.
As for other vitamins, IV therapy or injections seem perfectly reasonable if an individual has a severe deficiency in a given vitamin. Otherwise, just use oral supplements and tweak your diet to address deficiencies.
I had a course of B12 shots when it was discovered that I had dangerously low b12 despite having been primal for the previous year. I have celiac (which I didn't know until I went primal) which is not so good for absorbing vitamins and is linked with a condition called intrinsic factor deficiency (which I have) which limits the amount of b12 absorbed by the body as well. So after a course of 6 injections I now take sublingual B12 daily.
B12 injections are used for vegans, and needed who those lacking stomach acid or intrinsic facotr which are required to absorb B12.
Magnesium sulphate is also used in pre-eclampsia to bring blood pressure down, and does so VERY effectively.
Vitamin C is used IV to treat cancer with very good success, as there is a limit to the amount you can absorb through the gut.
IV vitamins and minerals are great if the body is weak and needs to heal, or if a condition means you need more than can be got through normal supplementation.