what exactly do you mean by GUI packages and GUI designers?
believe it or not, there still are tons of applications written in Swing out there, but since they don't reach the internet but are used in-house, you won't hear from them.
if you mean: is it worth it learning how to write a Swing GUI myself, while NetBeans can easily do all that work for my in it's WYSIWYG-editor, the answer would be:
1. using an editor sure is easy, but if you don't understand how the code is built, or what it does, than how will you control it?
2. ever browsed to elements in your GUI using the TAB-key? try doing that, if you added elements later, in a NetBeans created GUI.
3. what are you going to do when you start working in a company that hires you to write GUI's for their applications, but won't allow you to use NetBeans?
You'll never get past the absolute simplest simple forms without understanding how Swing code works. GUI designers are useful to get some simple layouts & listeners done, but you'll very quickly want more control and want to do more clever things, so you'll end up writing the code anyway.
My opinion is that you should write your own code until you have a good grasp of how it all works. After that you can use a GUI designer to speed up easy cases, but most pros will hand--code to get the exact results, maybe doing a little copy/paste from things they already have on their hard disk.
The one exception is if you are mocking up screen layouts as part of a cyclic design & review process, when a GUI designer can be a real time saver.
Thanks guys. I enjoyed reading your responses. I was under the impression it was better to learn by coding. I was surprised to see a GUI tutorial by Oracle that uses the Netbeans editor. This made me ask the question.
I personally prefer learning Swing. While GUI designers are great things to start with, I think that typing out the code yourself has greater benefits in the long run. Also, it is interesting to see how Swing works, too. Granted, GUI designers are real time savers if you need to get something done fast (Swing can sometimes be frustrating trying to get the correct layout), but I'll usually just type out the code myself. Of course as JamesCherrill mentioned, I do copy and paste a lot, but I guess that's just the nature of the beast.