Speaking as a (sometimes) freeware developer, it is nice when someone donates a little money to help with the cost of the tools used to make the software.
Just bear in mind that a donation doesn't entitle you to guaranteed bug fixes, enhancements or whatever.
Donate because you found the software useful, not because you expect something more in return.
We would hate to see the developer of Nutcracker not have any pixels himself to show off at Christmas
So if you use Nutcracker and have found it to save you lots of time or if you compare the effects that can be generated to other expensive professional software packages then a small donation is really not much to show your appreciation and support.