Peter Bromberg shares a MongoDB-based cache utility for .NET System.Web.Caching.Cache and some performance numbers:

The advantages of using such a MongoDb - based Cache are several-fold:

1. It can be accessed from any machine on a network
2. The cost is reasonable (as in “Free Beer”!)
3. The cache survives IIS AppPool recycles and even machine reboots.
4. Since it is designed to be able to implement the base OutputCacheProvider class (by just adding the required override keywords), it can be easily made to be a complete replacement for System.Web.Caching.Cache as described in the second article linked above.
5. MongoDB supports an automated sharding architecture, enabling horizontal scaling across multiple nodes. For applications that outgrow the resources of a single database server, MongoDB can convert to a sharded cluster, automatically managing failover and balancing of nodes, with few or no changes to the original application code.

via: http://www.eggheadcafe.com/tutorials/aspnet/93206c89-09c9-40fc-9296-7d74bb7996ad/a-mongodb-cache-utility.aspx