I guess it depends on what you consider site maintenance.
Over the years, the donations we receive go towards the operating costs of the site -- hosting, domain renewal, technical support, etc. If there's something that needs to happen to keep the site running, the donations go towards that.
More often than not, there are enough donations to cover the operating costs. Sometimes there is an excess, and that excess carries over for the next year. Despite excess carry over, however, there are times when there aren't enough donations over the year to cover everything. When that happens, I just eat it.