Relying on a default serializer.

Storing large objects in a single cache item

Using cache to share objects between threads

Assuming items will be in cache immediately after storing them.

Storing entire collection with nested objects

Storing parent-child objects together and also separately.

Caching Configuration settings

Caching Live Objects that have open handle to stream, file, registry, or network.

Storing same item using multiple keys

Not updating or deleting items in cache after updating or deleting them on persistent storage.