Can I browse the catalog to see which books are checked out?
Yes. It is possible to do an up arrow lookup on many non updatable fields such as the catalog panel field which displays "checked out" or "On Shelf". Just as the Tab key takes you from field to field for all updatable fields, pressing Alt-F2 will take you from field to field for all fields including those that are non updatable. When you land on the "On Shelf" field simply press up arrow for your lookup.