To be perfectly honest, I don't pay attention to how often the (Social Security Death Index) SSDI is updated at or at Ancestry. I search it at Rootsweb for two reasons: I like the interface and I can remember the URL (http://ssdi.rootsweb.com). Both sites have the same data (Ancestry requires a membership (or at least a free trial) to see the data). Rootsweb shows the same information for free.
Since I'm not often looking for the really recently deceased, I'm not overly concerned with how fast the SSDI is updated.
Out of idol curiosity, I checked Ancestry and Rootsweb versions of the SSDI tonight for my uncle who died in late December 2006. Both databases contained his entry (Roger Neill, 1937-2006 for anyone who is interested).