Always dispose a form

Some time ago, we noticed that in one of our projects the size of memory of our application is growing and it never decreased.

After some checking and testing we realized that even if we have a local reference to a form, if we haven't  disposed it explicitly it will remain on the stack and never be collected.  

So now, instead of writing this:

new usersDialog().ShowDialog()

We write: 

using(var dlg=new usersDialog())
    dlg.ShowDialog();