There is a lot of discussion right now within the postal service as to the future of slim jim size magalogs (actually all booklet type self mailers).

The concern of the USPS is that these pieces (when formatted correctly) qualify as either automated letters or non-automated machinable letters, but in most cases cannot be processed effectively on USPS letter sorting equipment.
 
The objective of the rate change and reclassification of May 14, 2007 was to better align the cost of mail processing with the actual mail category.  Because these pieces do not run well on letter equipment, often times they are run on flats sorters.

Because flats equipment is being used, the cost to process the mail is higher than the postage rates for letters can cover.
 
All that being said, there was an Advanced Notice of Proposed Rulemaking issued in the Federal Register on March 14, 2008 outlining testing that the USPS is conducting on booklet style mail pieces with different physical properties. 

The main components being looked at are thickness, tab integrity, cover stocks, finish size, and basic mail piece orientation.

Once the fate of slim jim magalogs is decided, we’ll make sure to update this blog with details.