I discovered another nice new feature today when creating computed columns, the PERSISTED keyword. In previous versions, to avoid the overhead of the calculation you could create an index to materialise the computed column. Now you can just persist the computed column and the result is stored with the table and updated as necessary. For example:

create table dbo.Tasks
(
    StartTime datetime NOT NULL,
    EndTime datetime NOT NULL,
    Duration  AS EndTime - StartTime PERSISTED
)

One other thing to note is that the PERSISTED keyword also helps you to create indexes on the column too. Remember that a computed column must be deterministic and precise in order to create an index on it. Well there are several ways in which that might not be verifiable in SQL Server 2005; for example with CLR functions. Persisting the column ensures its deterministic and hence allows index creation.