I can speak/read/type (I have awful handwriting) Mandarin to an intermediate level.
Since moving back to Hong Kong 2 1/2 years ago, my mandarin abilities have rapidly decreased, but they are in there, and get dusted off a few times a week.
Having found myself with some unexpected free time, I decided to take a month of intensive Cantonese classes in November 2013 - 4 hours a day, 5 days a week, for 4 weeks.
Why? Well, I live in Hong Kong, and my kids go to local Cantonese school. It will be good for them to see me studying Cantonese, and it will help me to communicate with the other parents and teachers at the school.
I don't have any expectations that my Cantonese will ever catch up with my Mandarin level. On the other hand, I perfectly expect to lose one Mandarin word for every Cantonese word I learn!!