I remember something in The Deathly Hallows that Harry tries "Accio Hagrid" and the bike shoots towards Hagrid instead of the opposite thing that should occur. (Thanks Himarm for the quote)
“Hagrid!” Harry called, holding on to the bike for dear life. “Hagrid — Accio Hagrid!” The motorbike sped up, sucked toward the earth.
So what would happen if we said, let's say "Accio Eiffel tower" (Not Accio moon as it may cause death due to various factors :D ), assuming that we don't have enough power to summon such a big object. (I doubt only Dumbledore could manage that! ). Would we get sucked towards Eiffel tower as harry and the bike gets towards Hagrid. Wouldn't that then be a great way to travel? ( If we can somehow manage to prevent collisions, by putting some spell on ourselves or something?)