They are only updated when the tile is requested (read "viewed"). So if you work a lot on the same area, the tiles are requested more and you get an updated NoNames layer.

Above comment is only for the rendered tiles. For the underlying data, it's normaly once a week but they've been having technical difficulties for a while : http://support.cloudmade.com/forums/general/posts/2681/show

You could try using Yet another validation tool: http://beta.letuffe.org/
It has an option for a Nonames layer, and it seems to be updated fairly often. See for more details: osm.wiki/Yet_another_validation_tool_for_osm_data