Last Friday I have taken the Microsoft Office SharePoint Server 2007, Application Development (70-542) exam and passed it with a nice 100%!
The exam itself is not that difficult. It might get tricky though if your company doesn't deliver solutions using all of the 6 SharePoint slices but is specialized in one of them like for example Web Content Management.
It's my first step on the SharePoint certification road. Coming Friday I will be taking another SharePoint exam: the Microsoft Office SharePoint Server 2007, Configuring (70-630). Furthermore I also want to become certified WSS developer.
Certification is important: although it's rarely a measure of your skills it means quite a lot for the customers who tend to have more trust in certified professionals.