Is there an easy way to export annexed files out of the repository? (e.g. to make a copy elsewhere, send a file by email...)
Sure, you can simply:
cp annexedfile ~
Or just attach the file right from the git repository to an email, like any other file. Should work fine.
If you wanted to copy a whole directory to export, you'd need to use the -L flag to make cp follow the symlinks and copy the real contents:
cp -r -L annexeddirectory /media/usbdrive/