If your laptop is probably connecting to public wireless network from time to time, so you'll want that shared folder on your desktop PC. Otherwise your shared folder might be visible to people around you. If you've setup passwords for both your laptop and PC, and I hope you have, then you should be reasonably secure on your laptop in public. (Win7 saw every folder on my network until I upgraded it to SP1).
Even though you probably have a wireless connection to your router that servers well for browsing, it's too slow for large file transfers so go with that ethernet cable, direct to the router when you're moving your files.
Hope this makes sense.