A friend of mine who was looking for a job, got joining offers from 4 good organizations. The ball was in his court now. He had to pick the one best suited to his aims and goals.
Also read Comparing two or more job offers
He came to me for the advise and I told him to accept the one his heart tells him to, but do not forget to inform the ones you are not joining. He seemed surprised and said "Why would I do that" the discussion ended and he decided to not pick up the calls from the companies he had decided not to join.
When he joined the organization he had decided to, he was assigned a project that was not relevant to his skills. No surprises, he could not perform. He was stuck. He had lost those organizations who had extended him an offer letter earlier. It was too embarrassing for him to call them back and check if the position was still open.
However, only if he had been courteous enough to inform them timely that he is not joining, things would have looked different. He could have gone to one of those organizations to check if they still had that position open. But now he was an unhappy, non performing employee who would probably not get a salary hike.
I have come across several such people in the past 8 years. I always say that only a brilliant person will have joining offers from multiple organizations. Turning an offer down is fine, but not informing them is not cool. It shows your attitude, attitude that you do not bother, that you do not care.
So if you at any point of time, have more than one offer in hand always remember to inform the one you are turning down. It is not easy to say no. You definitely need balls to do that. Write them an email or give them a call. The choice is yours. But inform them as soon as possible. The organizations do have deadlines and their projects could go on a toll if they do not have the resources at the right time. If you inform them well in advance, they will go ahead and hire someone else. They will thank you for that. Trust me on this, accepting the offer and not showing up is the worst thing you could do to an employer.
So, pick up that phone or better still send them an email.
All the best