• Click on the 'Home' tab in the upper left to go to the root of your site. 
  
• From the 'Add to folder' drop-down menu, choose 'smart folder'. 
  
• Leave 'Limit Search...' unchecked. (Unless your site will be huge, then check it and put 50 or 100, or whatever you like.)
  
• Check 'Display as Table' and add these columns: Title, Creator, Modification Date, Description.  (Note: Unfortunately, creator shows the username, and not the full name, of an item's author.)
  
• Click Save. 
  
• Click on the 'Criteria' tab. 
  
• In the 'Set Sort Order' box, choose 'Modification Date' for the field name, and check 'Reverse display order.'  That will give you a reverse list of all the items.

For our site, we didn't want container items like folders to appear in the list.  There is no 'not' criteria for content types, which means there is no direct way to tell a smart folder to filter folders out of the search results.  Instead:

• Add an item_type criteria.
• Click the 'Add' button, and then on the next screen, Ctrl-click the items in the list to include only the content types you want in your recent changes list.
  
• Make sure you have select 'or' as the 'operator name'.
• Click 'Save'.

You can create a recent comments list by following the same steps, but selecting 'Discussion Item' only when you add the item_type criteria at the end.  It would be nice to have the location listed in the table for comments, but on our site, this column was always empty, so we deleted it.