My husband and I both speak Mandarin, although we usually modify that phrase with a very heavy dose of qualifiers. It's a tough language to get really good at unless you're immersed in it. While we often speak Mandarin (or rather, our version of it) to each other, I'm fairly shy about using it out in the world. We do have opportunities to speak the language on a regular basis, but it is all too easy to slip back into English, so that's mostly what we do.
We were at a party the other night and someone asked about the language that is spoken in the orphanage. It is Mandarin, of course (although English is widely spoken in Taiwan so it is not a problem for English speakers to navigate the country), so this person was very astute in thinking that the sounds and rhythms of the language might be soothing to our little guy when we bring him home. Hubby and I have more than enough grasp of the language to talk baby talk (e.g. "Are you hungry?", "Are you thirsty", "What do you want?" as well as the more advanced, "No, you cannot take the car tonight! Go do your homework!"), but we're still brushing up on our Mandarin. Not only is it a good language for us to know, we'd love for our child to become bilingual (or possibly even trilingual - Parla Italiano?) and it's soooo much easier to learn a foreign language when you're young than it is once you reach a certain age (and by that I mean once you've reached high school ;-).
There are some fantastic resources for learning Mandarin on the web. One of our favorites is Chinese Pod. Their approach is practical and entertaining with lessons for every level covering tons of topics. Hao ma?