Cleanup guidelines?

When I programmed C++ I used class destructors very carefully and in those days it was just as important to cleanup after yourself than it was to write the program correctly.

But in .net no one seem to focus on cleanup code. I understand the concept of garbage collection, but I still find it a bit intimidating never have towrite any cleanup code...
What if I write a winforms app with lots of class declarations, arraylists, custom objects... an app that is thriving with the keyword "new"... and then I just close down the form. Will all the memory allocated then return to the OS? Are there any guidelines when to remove object references with the "nothing" keyword?
And is it good or bad .net coding to use the GC manually? Like running

GC.Collect() upon Form1_Closing event?

Most apps have a end button or something... what cleanup code (except obvious things like closing db pipes etc) should I but there in my .net apps? No books seem to really touch the subject.

kind regards
Henrik

This is probably the perfect article for you.

http://www.vbdotnetheaven.com/Code/Jun2003/2045.asp