1. Buy services(at NB) if you don't have money in USD or other currencies at the moment but have decent reputation and $$$$$NBs
2. Donate $NB to someone if you find his post, info or service worth donation
3. Give your friend/someone a surpise $NB lot you don't have anything to do at the moment and feeling too heavy with loads of $NBs (my user id is ChillingBreeze in case you didn't notice)
4. Donate $NB if you're ultra-happy with someone's service
5. You can give $NB if you are lazy to write a review for someone (Umm not very good idea though)
I got only these ideas for now.