Can Slopes Import My Data from Other Apps/devices?
Yes, along with being able to use Slopes to record, you can import data from other devices and apps. To do so email the file to yourself, tap the attachment, and pick "Open in Slopes." Slopes will process and import the GPS data as an activity.
If you're at your computer you can also use iTunes File Sharing to import a bunch of activities at once. Follow Apple's guide to get started.
Ski Tracks Imports
Files exported from Ski Tracks in the .skiz format can be imported to Slopes.
Trace / Alpine Replay
Trace can export to the common GPX file format via their web interface. Head to http://snow.traceup.com/settings/gpx, log in, and then you can pick which days to export. Get those files to your phone, try to open them, and you'll see the ability to open them in Slopes.
GPX files are commonly exported from other stand-alone GPS devices (such as a Garmin). Note that the file needs the following data to be included: latitude, longitude, altitude, and time. Data accuracy is improved if the file also contains vdop and hdop (vertical and horizontal accuracy) data.