What if it's April 15, and your ship is coming in next month... guaranteed, secured, insured, and enough for the contribution, and to get your cash reserve built.
Beverly did a great job with her article on this topic, though I think everyone's leaning toward (practically to the point of falling over) it not being a good idea. It was a very, very niche oriented idea that we all agreed had about the same chances of winning the lottery (maybe if you won the lottery April 14th, and the check didn't clear until the 16th, then go ahead and charge that IRA.)
One point I had hoped to make was the individual thinking about this obviously has nothing in the way of a cash reserve they could draw down and replenish. Goal #1 prior to the IRA might be to fund that cash reserve (and not on credit).