Workflow: Is there a limit on the size of the condition box in the workflow designer?

There is virtually no limit to the size the condition box of transitions and notifications.

WorkflowGen uses ntext in SQL Server and CLOB in Oracle to store the condition text.

SQL Server:

http://msdn.microsoft.com/en-us/library/ms187993.aspx

Oracle:

http://docs.oracle.com/cd/B19306_01/server.102/b14237/limits001.htm