Our Pack does a spring roundup for both re-registration of continuing Scouts and registration of new Scouts (mostly Tigers, but we pick up a few at other levels every year). We hand out the books, the summer newsletter, and whatever other information is at hand, and then basically say "see you in September".
Pros: we get a sense of how many Scouts to expect in the Pack in the fall, the boys get their books and can work on achievements and electives over the summer (especially the sports-oriented ones), and having their materials for next year seem to keep them interested over the summer. At least we very rarely lose a Scout who registered in the spring.
Cons: can't really think of any! Our Pack doesn't try to have a lot of summer activities, as there's just too much else going on (summer camps, sports, vacations, etc.) although we do hand out information on the local Cub Scout summer camps.
We also run a Fall Roundup to catch those re-registrations and new registrations that didn't happen in the spring.
Works for us, anyhow.