I finally got around to sitting the rest of the SharePoint certs.
They vary quite significantly in difficulty, here are my recommendations for people thinking about sitting the exams.
Windows SharePoint Services 3.0, Configuring (70-631)
This exam has a big infrastructure focus. Definately harder than its MOSS equivilent. Brush up on your network load balancing and authentication methods. Has some easier stuff on standard site configuration as well.
Windows SharePoint Services 3.0, Application Development (70-541)
The general theme with the development exams is that they are much harder than the configuration ones (of course :-).
You really need to know all the various XML schemas for this - feature.xml, elements.xml, onet.xml etc.
Microsoft Office SharePoint Server, Configuring (70-630)
I thought this exam was really easy. A lot of easy questions around content types and records management. Has a few trickier questions around Enterprise features such as Excel Services and Forms Server. If you use the enterprise features a lot this probably won't be a problem.
Microsoft Office SharePoint Server, Application Development (70-542)
Of all the exams this was the hardest. The questions are basically around doing stuff in the Shared Services Provider, but in code (eg add an audience). I would recommend having quite a bit of MOSS specific dev experience before tackling this one.