Why use patterns:

• patterns help us be more efficient
• patterns describe reusable solutions to common problems

Bulk Processing

• Caching
• create triggers w/ ability to process hundreds of lookups
• challenge: queries, DML, memory
• collect all keys from trigger object in Set Object
• Query once using SOQL in clause with key set
• cache results in map object
• look up related values using map key

Apex Summary Rollup

• Need to roll up from a child to a parent in a lookup relationship
• No declarative option for rolling up in a lookup relationship
• Identify parent IDs affected by change in child.
• perform an aggregate query on child records
• update parents using IDs

Configuration Abstraction

• Manage values that change from environment to environment
• Maintainability
• Ease of use

Pagination

• display records one page at a time
• performance and maintainability
• StandardSetController

Search And Sort

• Allows users to apply search criteria and column sort
• challenges: Performance and maintainability
• reusuable Apex and component framework for Search and Sort
• Dynamic SOQL to modify Where and Order by query clauses

http://developer.force.com/cookbook/recipe/trigger-pattern-for-tidy-streamlined-bulkified-triggers