ice dam - long lasting damage?

The lifted shingles will soften up and rest back in place come warmer weather...As for any damage, I would say that the worst case is water from melted snow flowing around the base of the vent going thru freeze/thaw cycles that could potentially cause damage to the seal around the vent and your roof that will cause leaks during rain storms in the summer and melting snow during the winter... Proper flashing around the vent carried out over a large surrounding area would prevent this, and as how you stated water was leaking into the bathroom you may or may not have a problem. If the water was running into the bathroom from the inside of the pipe, the flashing should be proper and the problem is simply too much snow. If the water was running into the bathroom from the outside of the pipe, it could be one of two things..

1. The water ran along the inside of the vent starting from above the roof until it reached the first joint where it began to travel on the outside of the pipe, As rigid vent pipes are assembled so that one pipe is inserted into the other from the source all the way until the exhaust... If this is the case, the flashing is fine.
2. The flashing failed or is non-existent and is allowing water to run in along the outside of the pipe....

Either way, Have a professional examine the situation and take the proper course of action... Always get more than one opinion, and if work is required beyond what you feel capable of, do what I do... Get three estimates detailing the work required, throw out the high and low and hire the person in the middle.

Grim

According to Hamilton Audio :

Since you cleared it promptly, as long as it drys out in relatively short order, there shouldn't be any permanent damage to the house. But of course you should inspect (or have inspected) the area around it just in case a bit of freeze/thaw wrecked some flashing, and get suggestions on how to prevent it recurring. And see if any of the drywall turned to mush.

But are you absolutely _sure_ it was an ice dam however? Did you get major ice buildup and water backup on the eaves? Or, a bit of ice, no major water pooling, and most of the signs of water were right around the vent and ducting?

Sometimes thermosiphon of moist air thru the bathroom vent can cause so much condensation dripping back down thru/around the ceiling vent that it can fool you. That's usually very easy to fix.

I don't see any sort of flashing around the vent itself. the vent has a large flange on the base, and this is fully intact and in good shape. the vapor barrier prevented the drywall ceiling from being damaged :)

Oh I'm positive. right below the outlet of the vent, you could see the ice building. about 4" down from the outlet it began to get bigger. then about 8" or so past that (just ahead of the eave) the ice was built right up, about 6" thick. the eavetrough was completely packed tight with rock hard, clear ice :( The signs of leakage inside (black staining on the sheathing boards) was well down the roof from the vent...

Oh, this is not the case (tho a good idea). clearly a classic ice dam situation brought on by the bathroom vent melting snow underneath an easy 14"+ deep snowpack!