Shoes
 

Is there a case to be made for cycling shoes? What is the matter with plain lightweight running shoes?

Cleats can't be attached to running shoes.

Running shoes don't have stiff soles to help avoid hot spots and to better transfer power to the pedal.

On long rides, the hot spots become significant for many folks.

This is truly the correct answer. I road for a long time in regular old Pumas and when I finally got a pair of Specialized touring shoes I could kicked myself in the ass for not getting them earlier. I still have those shoes and they are literally about 8 years old so it's a good investment...

If you ride long and/or hard then stiffer soles make a big difference. For just riding around town, running shoes are adaquate.
Many lightweight trail shoes do have stiffer soles, comparable with leisure cycling shoes.

If you get large enough platform pedals, and ride less than 20miles then practically
any shoe that can be comfortably walked in would be ok. Steve