However, if you ask me about software art or something serious, I would tell you that I would not use it for my projects (although I seriously considered NetBeans once).
- It is too much "IDE-ish". Even an attempt to "make it right" as Blue Marine project  still contains too vivid smell of plugin-based platform. To get rid of it smell you need to remove a lot of things. It will suck more blood from your body that you just do it all yourself from the scratch.
- Too heavy for JNLP. Even with one single "Hello World" plugin — almost 20MB.
- You need do unnecessary wrapper-works and other hacks-n-tricks in order to use Swing-X components. Why?..
- I don't like its Plugin Manager from user point of view (nothing wrong with it itself — works perfectly).
- Plugin mechanism is too heavy and can be simplified to much lighter incarnation. It gets better, but still there is way too much XML.
Personally, I vote for minimalism or, if possible, extreme minimalism. I love to remove everything, unless it is just impossible remove everything else. With NetBeans, still, you have some persistent bits that I would love get rid of it for ever.
One curious thing: an author of Blue Marine complained that first attempt was actually done on a solution from scratch and he was completely unhappy with it, therefore he revealed NetBeans for himself. In fact, I am opposite... — the World is that different! :-)
1. Frankly, I have just zero idea who needs this thing on Windows with Google Picasa, on Mac with iPhoto and on Linux with F-Spot... Well, but anyway somebody has a fun, right?