Well, I do every single month and within each, I get 20 MS Points, last month it was 40 MS Points. It's kinda fun too. They'll only dispatch the MS Points once it hits every 100 MS Points in total. Maybe I'll buy The Simpsons Arcade with the Free MS Points.
I do it when i remember, i still have 2100ms points that have been on my account for almost a year. Not really purchased much on the 360 for a long time, mainly been playing retail games.