They process returns in batches, so if you wait till the deadline your refund will take longer to go out due to the number of returns that they receive close to the deadline. Also, if you did not direct deposit your refund that also holds it up. If you filed on April 17th, then one month is not that long to wait.
I know the batch "process". Filed in late March. Should have recevied it by 4/17, it was then delayed to 4/24, then back to "in process", then to 5/1, then back to "in process", and now to 5/15.
We are able to itemize due to mortgage interest and charitable contributions to our Catholic Parish. Outside of that and my wife's lifetime learning credit for Grad School, we a basic return.
It shouldn't have taken this long.