Are there limits to how many users can view or download the same ebook at the same time?

Most NC LIVE ebooks have no holds and no simultaneous user limits, but a few collections do have limitations.

Collection Usage limits
Ebook Central Unlimited users
HomeGrown Ebooks Collection Unlimited users
RBdigital Unlimited users for classic titles; 1 user at a time for contemporary titles
eBooks on EBSCOhost Maximum of between 1 and 10 users, depending on the title. Newer titles allow more users.
Gale Virtual Reference Library Unlimited users
Testing & Education Reference Center Unlimited users
MyiLibrary Maximum of three users per title for viewing and downloading
Open Library One user at a time for every title