In my eyes, it makes it much harder for a President to remember what it's like for the rest of us that don't have secret service protection for the rest of our lives after becoming president.
Just to clarify this point. Clinton is the last president authorized lifetime Secret Service protection. Congress sent him a bill to that affect and he signed it. So neither Bush or Obama/McCain will have said protection after leaving office. Personally I think this is a really bad idea. I don't think any president in modern times will need it more then Bush with all the Islamic Radicals and Liberals he's been making friends with for the last 8 years.
The Secret Service could still get a special authorization to protect Bush same as foreign leaders or high profile US government employees but its not automatic anymore.