How many characters can a SQL Server 2008 database field contain when the data type is VARCHAR(MAX)?
From http://msdn.microsoft.com/en-us/library/ms176089.aspx
varchar [ ( n | max ) ] Variable-length, non-Unicode character data. n can be a value from 1 through 8,000. max indicates that the maximum storage size is 2^31-1 bytes. The storage size is the actual length of data entered + 2 bytes. The data entered can be 0 characters in length. The ISO synonyms for varchar are char varying or character varying.
1 character = 1 byte. And don't forget 2 bytes for the termination. So, 2^31-3 characters.