In reply to kmsands:
I worked out at Rothera as an Electronics Engineer.
It's worth noting there's a massive disparity in how competitive the differing job roles are. It's not uncommon for BAS to get around 2,000 applications for just four Field Guide positions. They're more interested in your attitude and who you are as a person, than having an MIA/MIC, etc. Some of the fieldies have no formal Mountain Training qualifications, but all have done a fair few Alpine summers, ideally with the odd trip to Kyrgyzstan, or the Greater Ranges, or time in Svalbard, etc. As Jim Carey says; "The effect you have on others is the greatest currency there is". You can have Scottish Winter routes coming out of your eyeballs, but if you can't get along with other humans, they won't employ you.
All the dive team and biologist positions are similarly competitive. You gotta compete with many hundreds of people to spend a year scuba-diving with humpbacks, studying penguins, seals, or albatrosses!
The Tech Services positions are typically less competitive, so if you're a qualified Plumber, Electrician, Generator Mechanic, Vehicle Mechanic or Vehicle Operator, you're in with a much better chance. Apparently the Gennie Mech position is the hardest to fill; they get circa 1-2 people apply a year! Qualified chefs are in with a good chance too, but it's a tough job!
In terms of the experience, it's mostly incredible, but as everyone says, it's a bit of an emotional rollercoaster; the highs are so high and the lows so low, but all is glorious in retrospect. Whatever you do, don't go out there if you're in a meaningful relationship; it simply won't last. Antarctica is like Big Brother on steroids, but an experience that lasts a lifetime.