As far as Hillmap goes... you can use it, but you do need to keep track of your runs or lifts, which could be a bit of a pain. But you'll be able to see a cool map of where you skied.
Here's a simple example... let's pretend I went to Whitetail, and skied each of the 10 main trails once. That would mean riding the EZ Rider Quad twice, the Whitetail Express Quad 5 times, and the Expert's Choice Quad 3 times.
If I knew how much vert each of those lifts was, I could just do the math. Since I don't, I can go to Hillmap and find the resort (you can search with search link in the upper right). It will look like this :
Now most resorts will also show color coded lines along the runs on the topographic map (as Google Maps does). Whitetail is missing this, annoyingly. Anyway, if you click on "Paths" at the top, you'll be in path drawing mode. You can draw any paths you want and get statistics and a topographic profile of it. For instance, if I wanted to check the main lift at Whitetail, and one of the blue runs, I might draw this path :
That shows that that lift and run cover about 895 vertical feet, along 1.25 miles. If I click the "Profile" button at the top, it pops up a window that shows the profile of the path, showing how steep it is all along the way :
You can see that the run I traced hovers around 20 degrees for the top two thirds of the run before a flatter section back to the lift. You could do this with each lift or run to find whatever vertical measurements you like. It would be simplest just to measure each lift, and multiply things out if you kept track of which lifts you rode.
Alternatively, you could trace all the runs you did, assuming you kept track, and really see that path you took. This would be a path taking each main run at Whitetail :
A total of 7842 vertical, and 12 miles of skiing. And here's the profile view :
With that many slopes, the profile isn't too useful, but I traced the greens then blues then blacks, and you can see the slopes getting progressively steeper.
Anyway, I think Hillmap is fun to mess around with, and seems pretty accurate (it's based on the US Geo Survey topographic maps).