I had a LOT of milk when DS was first born, but he was only drinking about 30 ml (1 oz) per feeding, every three hours, so I had quite a stockpile of milk in my freezer once he started nursing exclusively and we were done with fortifying milk in bottles! I donated it through Milkshare, and it was a really wonderful experience. I was rejected from donating to milk banks since I have to be on hypertension meds, and banks can be really, really selective, so milk containing ANY medications (even safe ones!) was rejected. I think I actually preferred the Milkshare experience! I know and got to select the families who got my milk, which was really hard when there are so many needy babies, but great when you've decided. I've got pictures of my milkbabies and am still in touch with one of the moms. I got to donate to 2 sets of twins, both former preemies, which was great. I loved it, and still do whenever I get updates on my milkbabies.
I did get blood work done just for the families' peace of mind, so I could send them the report showing that I'm HIV negative along with the milk. I know that I would want that as a Mama!
I'll be tandem nursing DS and New Baby, so it'll be a while, but I will definitely be donating again. I'll probably start pumping 2 or 3 times a day when New Baby is around 18 months or so, storing the milk, donating it when I have enough to make it worth the shipping costs for the family. I love donating milk, but also want to keep up a supply because we intend to adopt in the future, and relactating is way harder than building up a supply. And, I'll admit it, I love having the boobs that come with lactating, and will keep them as long as possible - and if I can help a baby in the bargain, so much the better
ETA: Most of the families I became familiar with on Milkshare were thrilled with a one-time donation - there was no pressure to become a constant supplier of milk for their babes if you didn't want to! They do ask for 100 oz or more, because it's really expensive to ship (has to be overnighted, and packed with dry ice), so I think one-time donations are fairly common.