Hiya,
Glad you like the idea.
Initially it was a response (as mentioned in the first post) to aid projects like the 'Parametric Browser Based 3D Modeler' as the guy is working on it part time.
At first, for something like that, that would benefit Shapeways and Users, Shapeways could have assisted its funding, and from there the general 'Donation buttton' thing came from.
As regards any 'specific' charities, none come to mind right now, but I suppose one could be 'The Heart Foundation', awareness of which could be emphasised with Valentines designs for example.
I wouldn't like to suggest anything specific to 'choose' from, other than the ability to link in, via the Donation button, a Charity/Person/Organisation of choice. Also to the degree that, per store, you can add as many as you like (ie: not just one button per store - You should be able to assign a different Donation button per design).
In the Account page I would like to see an editable list of the Charities/Organisations/People for this purpose, and then on the 'design' page the option to choose whether or not to assign a Donation button and if so you can pick from the list you created.
From there you would decide on a percentage or a set amount to be forwarded from the profit.
If Benjamin Nortier, for example (he of the 'Parametric Browser Based 3D Modeler') had a Paypal button that link could be 'integrated', or maybe there is another way?
Some Schools may benefit from this in that parents could assist in fundraising via this option.
Cheers,
Luis.