When my house was built (about a year ago), the contractor used rigid metal pipe up the wall cavity (2x6 cavity to accommodate the vent) straight up to a roof vent. The total length of the run is about 10-11'. The vent has a "flapper" in it with a rubber or neoprene seal to keep the weather out. I think the vent is actually designed to exhaust bathroom fans, but seems to work equally as well for a dryer. The only modification was to remove the screen on the outside that helps to keep the larger critters out; otherwise it just turns into another lint catcher. I have not had any problems with lint on the roof nor ice buildup nor condensation.
I could be wrong with this, but I think on a short run like that the heat from the dryer keeps the water vapor from condensing until it gets exhausted outside, at which point (even on the coldest days) it just dissipates into the air? Anyway, I don't know if this is the "right" way to do it, but it seems to be working quite well and I haven't seen any ill effects (yet?).
Here's a link to the vent they used: http://doitbest.com/Dryer+vents+and+...sku-261567.dib