Basics: iTunes U has LOTS of curriculum material created by educators categorized by subject area, submitting institution, and grade level. All the material is vetted through the submitting organizations, mostly Colleges, Universities and K-12 Education groups. There is a Beyond Campus area that also has materials from museums, libraries (think Library of Congress!), and other educationally minded organizations. Best of all - all material is available for FREE.
Educational Use: iTunes U is all about education as a majority of the information has been created by educational institutions. Find the material needed to introduce, reinforce or supplement topics you are teaching about. If you are in a situation where your students have the devices, as a teacher you can now push out the material you choose within iTunes U to the student devices using a common Apple Account (as long as students leave it logged into that account... Please note: don't share the account password with students as it is an account that works in the App Store, iTunes and iBooks!!)
Drawbacks in Education: The biggest drawback used to be that it was housed inside the iTunes Music Store. But, now that it is available as a separate app on mobile devices it takes away the fears that tech departments had in having iTunes open to access iTunes U when in a controlled environment
Cross posted at WaffleBytes