The Facebook login will require your user name and password (optionally; once "verified" you can turn off the password requirement, and simply check "DNA Login" on the login page), and then you will have to do the DNA Login. What this will do is sample your DNA (from a quick, mostly-painless blood test), send the DNA information to a DNA server site/service for ID analysis, and then send the ID confirmation to the Facebook login page. The DNA tester will discreetly dispose of the sampled blood via a vaporization technique (puff of smoke, slight "burnt blood" odor that will dissipate quickly and should not cause any smoke detectors in the vicinity to alarm), so you can be assured of your privacy from the machine once you leave (i.e., there won't be any leftover traces of "you" that a potential hacker could use to gain access to your account). Fancier systems will include "auto-sterilization" techniques, while more basic systems will require you to manually sterilize the test area before use (keep some Clorox® Disinfecting Wipes handy!). It is also possible to keep your own, private DNA analysis equipment, as portable models are expected to be available when the system is rolled out (being USB devices, they should easily plug-and-play with any system where you want to log into Facebook).
In some respects, this will simplify the login process for many users (who will opt to turn off "name/password" login requirements once verified). However, the DNA testing equipment and service will be a new experience, and for some, could be more costly than the value of the free services they allow you to access. Note: Facebook has no plans (at this time) to charge for any basic or premium account services, but it is believed that they will offer their own DNA analysis service at an as-yet-undetermined price. The DNA analysis service will likely initially come in two basic flavors: pay for equipment and pay for service. In the former scheme, you will buy the DNA testing device (while prices have yet to be announced, it is assumed that they will be more expensive than the simpler glucose testing devices available to the medical community; likely the initial hardware prices will be in the $1000-2000 range), and complimentary ID analysis services will be provided with the purchase. In the latter scheme, you will pay per month for the ID analysis service, and the device will be provided free (or at either a reduced cost or with a monthly rental fee included in the monthly service cost). It is expected that a large number of the devices, especially the portable devices, will also provide Bluetooth connectivity so that you can continue to log into Facebook via your smartphone's browser. There may be different pricing schemes available, but these are the first expected to be offered to customers. Also, the cost of purchased units will likely fall, especially as production and competition increases. Many cell phone carriers are expected to start incorporating the technology into their smartphones as well, although it will likely be mid-2012 at the earliest before devices with built-in DNA testing capabilities are available (HTC and LG are rumored to have already started working on incorporating the DNA analysis technology into an Android-based smartphone).
While the increased security and privacy benefits will be great, it is anticipated that many users will consider this an invasion of their privacy, and will consider dumping social networking services that decide to use this new privacy/security method. Facebook will be the first of the "social networking giants" to make this technological leap, but it is expected that Twitter and Google+ will follow very quickly. Yahoo!, AOL, and others will likely be slower adopting the technology, but will inevitably roll it out in mid-2012 as the prices drop and availability increases (Yahoo! and Google will likely "roll their own" - it is unknown at this point what compatibility issues may exist, but Google will likely be an open-sourced endeavor, and may already be participating in the DNA Universal Metadata Board, or DUMB, that is working on a common DNA ID Analysis Spec). Further, it is expected that DNA ID Analysis will become a new de facto security standard. For instance, once Google+ has run its trial of the DNA Login, it is expected that all Google accounts will incorporate the technology, from GMail to Google Docs to every little service Google provides. Yahoo! will likely do the same.
In fact, once the "social DNA ID experiment" has had some time to run, and feedback obtained, we expect that many financial institutions will adopt the technology for their banking and credit logins. We may even see DNA ID technology start to be incorporated into devices such as ATMs, self-service checkout kiosks, and magnetic card reader stations (e.g., your favorite check-out line, gas-station pay at pump screens, etc.), providing positive confirmation of identity before allowing transactions to proceed (this may become a burden to the users, as they'll have to have every family member that can use a particular card to be DNA tested and added to the card - a simple PIN will no longer be sufficient). However, this may offer an unseen benefit: you may no longer have to carry your card with you. Once DNA ID technology becomes fairly widespread and commonly used, financial institutions may make the switch to "DNA ONLY" services. That is, instead of swiping your card and using your DNA as ID confirmation, you may provide your DNA ID and then be presented with a list of "attached accounts" from which you can make payment. And, for those who have their own portable DNA tester, you will most likely be able to simply plug it into the machine (if you're paranoid about the sterility of the "public" DNA test module). However, this widespread adoption is not expected to occur until at least 2013 at the earliest. Of course, some believe the earth (or at least the majority of the human population) will cease to exist on Dec 21, 2012 (the link actually goes to a discrediting article - do your own research!), so widespread adoption may never come to fruition.
Yes, this is only a joke - a social experiment of my own; I hope it has amused you!