If you don’t want to share your power data with the world, it’s now possible to have the power data of your rides stripped from the ride files that are uploaded to Strava. There are also options to remove heart rate and cadence data. These new options can be found on the linked accounts page.
This works by creating a new TCX file based on the ride file was uploaded and uploading that to Strava. If none of the data stripping options are enabled and your ride is a FIT, TCX or GPX file, then the original ride file is uploaded to Strava. If your ride is one of the other file formats that Cycling Analytics supports, a converted TCX file will be uploaded. TCX files don’t support temperature data, so that is lost in the process.
On the topic on importing and exporting rides, a number of people have asked about automatic importing from Garmin Connect. This isn’t yet supported, and the main issue is that Garmin charges US$5000 to access this. When this doesn’t seem like so much money, I imagine that this will be added to the site.
This is the blog of Cycling Analytics, a website that exists to help people analyse their rides and manage their training. You might be interested in following via Facebook or Twitter. Also, I'm on Twitter as @cyclist_dave.