Should I close my objects and/or set them to nothing?

If you open an object, you should always close it (if it has a close() method), and destroy it by setting it equal to nothing (in JavaScript, var objectName = null;). 
 
Doing so helps ensure that you won't leave phantom objects hanging around in memory, taking up resources, without any chance of being used. IIS 5.0 is much better about garbage collection than previous versions, but you should always follow sane programming practice -- always destroy your objects. 
 
Also, with IIS 5.0+, the earlier you close your objects, the earlier the resources get released. This undoubtedly leads to better overall performance of your web server. 
 
(This is an improvement over IIS 4.0, where an object would be retained until the page went out of scope.) 
 
This question gets asked a lot, and my kneejerk repsonse is, invariably, "what do you gain by NOT closing and destroying objects?"