How often do older XBLA games go on sale?

I figured I'd go back and play a few older XBLA games like Braid and Shadow Complex, but I'd much rather wait until the price drops a bit. I swear I saw Shadow Complex for 560 points a week ago.

I think it's more of a random special offer occurrence than anything from what I've noticed. Unfortunately if you missed a price drop it probably won't come back around for a while :\

Yeah Shadow Complex and a whole bunch of other great XBLA titles were on sale last week.  I was waiting a few months for some form of price drop on SC to buy it, so not sure when one will roll out again. Though it's summer and hopefully it won't be too long!

I dont think its a 'random' selection, and its not always (although like 99% of the times it is) arcade games. The odd time I've seen normal 360 game add-ons on sale, avatar stuff ect. 
I believe Major Nelson makes a post once a month showing whats going on sale.

What Microsoft should do is have their week long blowout sales at the end of every month.  That would be fucking awesome.