James Howey of Microsoft gave us a very thorough explanation on the differences between a GDR and a QFE, what happened in SP2, and how to decide which build you should be aiming for.  I'm going to post it here, unedited.

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We recently posted updates to address an issue in two SP2 Maintenance Plan tasks. The KB article describes the symptoms as follows:

FIX: The Check Database Integrity task and the Execute T-SQL Statement task in a maintenance plan may lose database context in certain circumstances in SQL Server 2005

In Microsoft SQL Server 2005 Service Pack 2 (SP2), the following tasks in a maintenance plan may lose database context in certain circumstances:
. Check Database Integrity
. Execute T-SQL Statement
For example, if a Check Database Integrity task is configured to check integrity on multiple databases, the task repeatedly checks the default database.

For the Execute T-SQL Statement task, this problem occurs if the following conditions are true:
. The Execute T-SQL Statement task contains multiple batches.
. The batches are separated by the GO statement.
. No batches use the USE statement to specify the database.
. The statements in each batch do not contain the database name.
In this scenario, those statements in the second batch and in succeeding batches will be executed against the default database.

This fix is shipped in two different packages:
. The GDR release is available via http://support.microsoft.com/kb/934458
. The QFE release is available via http://support.microsoft.com/kb/934459

What is the difference between a GDR and QFE release? GDRs are a new means of providing support. GDR fixes are reserved for those issues identified by SQL Server support as important enough to install on every instance of SQL Server. QFEs are used for the majority of fixes where the effects of the problem are not widespread or severe enough to warrant a GDR.

GDRs and QFEs are associated with certain build numbers. Build numbers 3043 through 3149 are reserved for GDR releases. Build numbers 3150 and up are reserved for QFEs. By reserving lower build numbers for GDR releases, users can continue to take advantage of GDR fixes, without having to install QFEs, which aggregate all the fixes shipped since the most recent service pack. Once a QFE is installed, GDRs will no longer update your system, because the build number is too low, and you have to install QFEs to pick up new fixes.

Why is this fix a GDR? This fix was promoted to GDR because users that relied on the Check Database Integrity task to validate their databases were not informed of database integrity issues that they expected to be detected.

The fix also addresses issues in the Execute T-SQL task, but, since these issues typically lead to script failure, duly noted by SQL Server, the T-SQL issues alone were not enough to justify the GDR.

Those users who now, or in the future, rely on the Check Database Integrity Task or the Execute T-SQL task in a maintenance plan should install the GDR.  Others may skip the GDR.

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