I understand your frustration, but unfortunately Marty needs to place adverts to enable him to pay for the servers.
It is always his intention to keep Orchid Board free and it's so great that orchid board is so popular, but that success causes a problem that we need better servers. Only a few months ago a new server was put in place which was a stretch to afford.
While some people donate to help there is not enough money raised that way and so the only way to fund the running of the site is to put adverts in. Marty doesn't get much say what goes in the adverts, it's a service from Google which pays the website to display it. What you see depends on all sorts of things, such as where you are in the world and what key-words are on the page you are viewing (hence we see lots of adverts for Orchid/plant related things because that's what the sort of words google is picking up on our site).
It is unfortunately that it causes problems on slower connections, but it is impossible to run a site for free without having some way of raising the money needed.
I must admit on my connection I don't notice it, even when I'm not logged in and therefore getting the adds, but I know what it's like working on slow connections when I have to connect to customer sites which can be infuriatingly slow. Unfortunately I don't think there is a way arround it.