If you are developing applications for the next generation of Server software, namely, Windows Server 2008, I'd strongly advise you to take a look at http://microsoft.mrmpslc.com/InnovateOnWindowsServer/Default.aspx.
By taking part in the Innovate on Windows Server program, not only does it give your applications, as the developer, the logo for delivering a certified solution, but it also gives your customers peace of mind, that this solution will integrate with Windows Server 2008 seamlessly.
So, the question is, can you afford not to get your application certified, when a competitor might?
You can get all the info you need at http://microsoft.mrmpslc.com/InnovateOnWindowsServer/Default.aspx which includes:
Both of the programs above ('Works With and Certified For') are beta programs, as Windows Server 2008 is still in development, but you can still enroll for the program by following the links above. The enrollment period only opened on 1st November, so you've still got plenty of time.