Sure, donation is a symbolic token of appreciation, and I will be glad to see NetBeans doing the same.
So, I agree with you, except that I want/expect to see donation pushed higher.
As far as I read, some open source projet owners have expressed their serious doubts about donation process, because it does not attract a lot of attention. 'Donate" buttons on open source web site projects have very little success. May be it's due to the success of open source: these days, a lot of open source projects are used in every Java development... Few developers pay attention to the life of open source projects as most of developers think they are part of the landscape: nothing less, but nothing more too.
So, I have think about it and my idea is that more donation is a matter of involvement, a matter of participation (read my posts mentionned above for details).
My conclusion is: donation as a token of appreciation is quite good, a very good idea, it's a level of participation. And well, IMHO, this level of participation, this ratio of participation, may be higher if donation gives vote rights, project lifecycle and orientation, and even, manpower.
Well, it's a matter of experiment. Maybe one day, one is going to follow ideas I have expressed in my posts, or will have ideas close to mine. And we will see if this higher level of participation is better or not. And if better, it will spread quickly.
I am eager to see these days.