I guess my answer is 'It depends'. It depends on whether or not the guests are going to be staying overnight and hence, have a lot of stuff. It depends on the weather, too. If it is summertime, I'm more likely to go out and help them cart stuff in. If it is wintertime, I'm more likely to meet them at the door and take their stuff from them if they need to go back to the car for more. Mainly so I don't have to take shoes on and off.
If none of the guests are staying overnight, it depends on whether or not they are the first guests to arrive. If they are, I'm more likely to meet them at the door and greet them, since I've probably been waiting. I won't stand there with the door open, though, since one of the cats likes to escape. If they aren't the first guests to arrive, I'm more likely to be busy visiting and will wait for someone to ring the doorbell and I'll go greet them at the door. Although, with my group of friends, they are more likely to ring the doorbell or knock and then try the door. If it is unlocked, they'll come in and holler. And since I can see my front door from practically anywhere in the house, this works great. The only time my door would be unlocked would be during a party.