The first post from the account came only a few hours ago, but there are already 80,000 followers signed up.
One of the questions that people have had with the Mac App Store was the question of “discoverability” of apps on the store that aren’t “featured” or on the “top” lists; hopefully this account will be one more way for Apple to get the word out about new apps that you might not otherwise hear about. If you aren’t a Twitter user, you can always follow the RSS feed for the account. If you’re on Facebook, App Store is there, too.