How good is FreeBSD as a development platform?
FreeBSD is an awesome hosting platform for live environments, however Java has been a thorn in its side for quite some time. However it appears this is no longer the case although installation is not trivial.
You have to get the JDK source from Sun, then apply the FreeBSD patch set from http://www.eyesbeyond.com/freebsddom/java/jdk16.html, and then compile.
More information: http://www.freebsd.org/java/
Once you have the JDK, running Eclipse and other Java applications should be a lot easier, but I don't know about SWT for FreeBSD... anyone?
You can get binary distributions of Java from the FreeBSD Foundation, they signed an agreement with Sun for that. Art from Java, FreeBSD is awonderful development platform with every language and environement you may need/want. Disclaimer: I've been a FreeBSD developer for more than 13 years.
I've always found FreeBSD a wonderful secure hosting environment, but perhaps not the easiest development platform. You will have to dig a bit to get Java 1.6 up and running, though I think it will be doable. I hope you are familiar with emacs or vi. The ports system will afford you access to many pieces of software, but they will have to be compiled from source code. If you are familiar with standard Unix command line tools and the command line itself, you should have no problems with FreeBSD.
Alan
Putting the actual issues with Java and such aside, the real question is what are you developing for.
If you are writing rich desktop applications, then you naturally want to develop on the platform that is most popular with your users -- and I'm pretty sure that can't be FreeBSD.
If you are developing web applications, then you want your development server to be as close as possible to your production hosting environment. If you are going to deploy on FreeBSD, then it might make sense to also run it locally, at least in a virtual machine. (Browser testing, of course, is a different issue.)
Do keep in mind that, while all development tools you can run on BSD are also available on Linux, the opposite is certainly not true, especially since Linux has gained more commercial traction.
All this being said, the best way is to see for yourself: try replicating your development environment, whatever that might be, on FreeBSD. If you succeed (and you're coming from Linux, heh), once you get coding you won't even care what OS you're on.