I want credits if someone uses something of my work. ( I don't care for the license )
If he wants to use it without credits, he must contact and ask me first.
Glest uses GPL for the sources but a very unclear copyright for all the models/arts. For the models/arts license they simply say "use it as long as you credit us". This very uncommon way of stating the copyrights results in a lot of trouble for linux maintainers and so on and this is the reason why glest is often marked as "non free"
Thats the reason why I decided to give a clear copyright (GPL matching to the glest code ) to my models, also GPL is really not a very good choice for models/art because the license was made for source code.
But I also have made some things that I explicitly marked as public domain. These can be used by everyone without credits and so on.
For example all my texture related photos at
http://www.burningwell.org are free to use. You can even say that you made them ( but thats really not very nice ).