The upgrade exam in my experience is considerably easier than the full SCJP 5 exam. I had the free voucher from SUN because I took the
SCJA. I took the SCJP 5 full exam and got 57%. I waited two weeks and took the upgrade exam instead and got 67% even though I really didn't prepare much.
On the initial version of the exam, I got butchered on the Collections - Generics and Threading section. The upgrade exam threading section is not nearly so complex.
MCPD (Enterprise Application Developer, Windows Developer, Web Developer - .NET 2.0), MCTS (Windows Apps, Web Apps and Disbributed Applications - .NET 2.0), MCITP (Database Developer & Business Intelligence Developer - SQL Server 2005), MCAD, MSCD.net, SCJP 5, SCWCD 1.4, SCBCD, SCMAD, SCDJWS, SCJA