Though I haven't looked at the Irish or the Hebrew in over a month, I do a little French, and sometimes some Spanish and/or German nearly every day, and I love it. I'd be perfectly happy never to have to solve another equation in my life, but languages come easily to me, and finding a free program was a great way to revisit the languages I haven't looked at since high school, and to bring my daughter along for the ride.
As it turns out, my daily Duolingo is like a healthy food I actually like eating -- delicious and good for me, too. I like the challenge and enjoy trying to develop my budding Spanish accent and recapture the accents I had when I took French and German decades ago.
I seriously doubt I'll go back to Hebrew, but I am considering dabbling in Italian.