Abstract Factory vs Factory

There are numerous post out there to explain the differences - i just wanted to add on

Factory - encapsulates the logic of creating a concrete type
Abstract Factory - encapsulates grouping of related factories.

I always start with Factory pattern first to decouple the creation logic from client.
So when will we go for Abstract Factory - as soon as your factory method violates Open/Closed principle. If your Factory method contains lots of 'if/else' or 'switch' statements, then it is time to move onto Abstract Factory. Please refer this article.

Also DBProviderFactory is another example of AF pattern. SqlClientFactory, OracleClientFactory, OleDbFactory are all grouped under DBProviderFactory.

http://en.wikipedia.org/wiki/Abstract_factory_pattern
http://en.wikipedia.org/wiki/Factory_object
http://msdn.microsoft.com/en-us/library/dd0w4a2z%28v=vs.80%29.aspx