There are multiple issues by having the majority of our books arrive in June and July (besides overloading acquisitions and cataloging). The biggest challenge I see is one of perception. Our students and faculty are on campus September to May. They only see a small number of new books coming in during those months. I'm sure that our students never realize how many tangible books come in over the summer, because they are already processed and shelved by the time they are back on campus in the August.
I have some ideas on how to even out our work flow, but I'm always looking for good ideas that work. Feel free to share what works on your campus by writing a comment (it won't show until I approve it).