Great idea Dani to add a premium sponsorship program. Lots of the bigger folks are doing it, and I think it's a great way to bring in extra revenue.
About the wording - should a commercial site - one that clearly generates revenue by advertising - use the specific word "donation"?
"A donation is a gift to a fund or cause, usually for charitable reasons."
IMHO opinion, the word donation should be substituted for something that does not imply "charity". I think subscription is more appropriate.
Also, many sites offer paid memberships for the privelage of surfing in an ad free environment. Any plans for a "platinum" membership level?