Learning/remembering Chinese I lived in China for a few months and picked up quite a bit of Mandarin. Now that I've moved back to the US, I have forgotten the Chinese I knew and spoke while there. Other than actually living where they speak Chinese, what is one of the most effective/efficient ways to learn Chinese (semi-quickly) and retain it? Software? Community classes? Watching/listening to Chinese media? Any suggestions of places to go to learn?
In my experience, taking a class, and watching/listening to Chinese media truly helps. 
I have taken classes on Chinese, and Chinese media can test if you understand Chinese. Using media also helps you "exercise" your brain; much like taking a jog once in awhile.

In order to retain knowledge on the Chinese, you should practice saying the word, or at least use them once in awhile. It's easier to remember the words with constant/common usage.

I would not recommend software; one problem I see is that if you have a question, you can't ask your computer. With a teacher, on the other hand, you can ask them questions and they can explain. It's a great time saver.

I'm not sure about any places you should go to learn, unfortunately. It greatly depends on what your age is, where you live, and your schedule.