There is one very large pitfall with ADSI scripts under ASP that is very easy to fall into. ADSI scripts running under ASP work only when served from IIS. This is because IIS understands ADSI, and IE on its own does not. So whenever you want to test-run an ASP incorporating an ADSI script, make sure that you are obtaining it from the server. This problem tends to occur in two main ways:
When developing scripts on the machine that IIS is running on
When developing scripts on a machine that has a drive mapped to the directory on IIS where you are storing the scripts
In both of these cases, it is just as easy to open a file called C:\INETPUB\WWWROOT\MYTEST.ASP as it is to open http://www.mycorp.com/mytest.asp from within IE. Both files will open correctly, but only the IIS-served page will correctly work with ADSI. If you start getting unexplained errors with code that you know should be working, just check the URL of the ASP that you are opening.
The second annoying pitfall occurs when you are constantly updating pages, testing them with a browser, and then updating them again. If you are developing in this cycle, remember to keep refreshing the page. It becomes really annoying to find that the bug you have been trying to solve is due to the fact that your browser thoughtfully cached a page 15 minutes ago, and you have been forgetting to press the Shift key when clicking the Refresh button.
 Another option if you are using Internet Explorer is to open up the Internet Options from the Tools menu and set the Temporary Internet Files to check for newer versions of stored pages on every visit to the page.