Best thing to do is keep the stanchions clean between rides to prevent scoring of the ano surface and contaminayion of the seals/fluid. I would say that in BC, you would want to open them up and change the fluid every 200 miles or so. Its important to use a really good quality brand of fluid. Gold Spectro is my favorite. You can really tune the ride of your forks a ton by fluid hieght and oil viscosity. Just keep in mind to follow your manufacturers specs.
BTW, its very important to change the fluid regularly as it breaks down during use and gets crud in it that can compromise your seals. Marzocci seals are super easy to change, but still require more hassle then a fluid change would. Most manufacturers also recommend seals be changed yearly. I do mine near the end of spring, that way I get thru the worst crud of fall/winter/spring riding and have nice fresh seals in the late spring/summer to ride with.
Thats about it, I love open bath systems for the simplicity.