Under the revisions tab for my recent activity, the "today", "yesterday", etc. buttons seem to be retrieving edits to my posts based on the timestamp that the post was made, rather than the timestamp of the edit.
For example, if I click on "last month", I should only see June 2009 edits. But I see four edits from July. All of those edits were made to questions or answers that I posted in June.
Another example: I have to click on "last week" for it to show an edit from nine minutes ago (since the edit was to a post made last week). It doesn't show up when I click on "today", "yesterday", or "this week".
Edit It looks like this has been fixed at some point (maybe when all the changes for the envelope notification were put in?).