I've always liked languages but made poor choices when it comes to studying genealogically relevant ones. Unfortunately, the language I chose to study throughout high school and college (French) doesn't help me with my genealogy research. Likewise, my year of Spanish won't do me much good when researching my ancestors. My desire to read and understand the languages of my ancestors have made German and Italian educational priorities for me.
Right now Duolingo offers English speakers courses in Spanish and German (yay!), as well as recently released, currently in Beta testing, French. I signed up for German and have also been brushing up on my French for fun. When Italian is offered in the future, I plan on learning that as well (hopefully, the Latin I took in middle school will help me out here!).
So why exactly do I want to learn these languages when I could just use a genealogical cheat sheet for records and such? For a variety of reasons, some of which are: 1) I want to be able to translate whatever I come across (like the letter in German my great-great-grandfather wrote), 2) I want to read and understand materials my ancestors might have come across or that might help my research in the actual native language, 3) if I want a record from Italy, like my great-grandfather's army records, I can just sit down and write for it, 4) I want to be able to communicate with non-English speakers if I need to, like the archivist in Germany or a new found cousin in Italy. I would also like to one day be able to work on more non-English record batches through FamilySearch Indexing.
Do I expect to become fluent using Duolingo? No, but I hope (and believe) it will provide a foundation on which I can build. I also know this will be a process and not something I'll accomplish overnight - but then that is half the fun of learning a new language!
One caveat, right now Duolingo is invitation only. I signed up for the wait list some months ago and only just got my invite a few days ago. However, I imagine
Update (as of 5/23/12): Duolingo is going to go public on 19 June. If you can't wait that long, contact me and I'll give you an invite.
Disclosure: I have no affiliation with any of the people, companies or websites mentioned and linked to in this post, nor did I receive any remuneration for writing this post by anyone.