In this post, Paul Stovell is categorizing the different ways unit of work might be managed in WPF applications.
Source: Paul Stovell's Blog
When it comes to dealing with databases, smart .NET developers follow the unit of work pattern. In NHibernate, the unit of work is an ISession. In LINQ to SQL and Entity Framework, it's the DataContext/DbContext.
When implementing a unit of work, or in fact any object, lifetime matters. When is the unit of work created? When does it end?