Also, will any problems (or benefits) arise from developers adding "use" statements for the same CPAN modules in their own programs?

I've tried a SuperSearch with no luck, just to head that off.

No, it's fine -- they only get included once. perldoc -f use says that use Module LIST is exactly equivalent to BEGIN { require Module; import Module LIST; } and perldoc -f require says that 'the file will not be included twice under the same specified name'.