Probably as often as the data provider(s) that Google is feeding into their system as well. You didn't think that Google was actually collecting that info directly, did you?
I believe he answered your question as well as could be done without some inside knowledge. We don't know how often anyone's db is updated, so with no benchmark how can a fair comparison be made?
I have no idea. When I start having problems with finding businesses, or if it takes me to closed businesses, I'll worry about it. So far, in over 2 years using the app, I've not had problems.