I recently received an invitation to a concert in my email. The invitations were managed by the online service Evite. The system keeps track of who's going and who isn't. A closer look showed you can even elect to join a carpool. At that time I was undecided about my attendance so I held back from replying. And promptly forgot about the whole thing. When I checked my email again two days before the event, I discovered the system had sent additional reminders to my email. Going back to the invitation page showed about 50 people said they would show up, 3 wouldn't, and over 300 people yet to reply. Having made up my mind to not go, I decided to join the 300 people and left the website without replying. Better to say I missed the email than to explain why I don't want to fork out $15 for a concert I might not like and with no prospect of meeting someone familiar.
If instead my friend invited me over the phone I would have to make up an elaborate excuse, or would even decide to go. So you see there is a difference in response depending who is asking the question: a machine or a person.
I am not trying to dismiss systems such as Evite. These systems are very useful when managing a large event. Computers (or machines in general) are very good at keeping track of things, doing repetitive tasks and they also scale well. Imagine the difference between manually calling up 50 people and 5000 people. For the computer, however, it is still just one click. There is definitely a good reason to use a computer-based system to help manage social events.
Where machines fall short, however, is the responses they get from clients (e.g., the invitees). In the example I have given, I was a "not yet reply" even though I was definitely not going. Most of the people on the invitation list also failed to reply. I cannot say for sure, but people may have given the invitation less thought because it was sent out by a machine to their email account. Additionally, because the entire reply process is managed by a computer, some people may have ignored it.
We definitely treat a computer and a human being differently, even if they are performing the same interaction with us. Sometimes I would add an item to the "shopping cart" just to find out the shipping costs and other info not present in the product pages, even though I never intended to buy the item. Now how many people will deliberately bring a product they will definitely not buy to the checkout, and at the last possible moment tell the store assistant they don't want it? We also feel less guilty lying to a computer. When I applied for Pandora, I just used a random US zip code to "prove" I live in the US. Had the signing up process been conducted over the phone, I doubt I would lie so readily to the operator.
In conclusion, computer systems are very efficient at managing social events and/or collecting information from correspondents. However, it seems they can seldom evoke a sense of urgency and at times even honesty like a human can. In some cases it is in the interest of the correspondent to reply promptly and honestly (e.g. to prevent fines or committing fraud) and the above doesn't matter too much. In less formal occasions a person can probably command a more timely and accurate answer than his electronic counterpart.