There are any number of spreadsheet apps available for the iPad, but recently the market changed dramatically when Microsoft released the full Office suite for iPad, including a version of Excel ... Microsoft Office 2007 Service Pack 1 was released on December 11, 2007. Official documentation claims that SP1 is not simply a rollup of publicly released patches, but that it also contains fixes for a total of 481 issues throughout the entire Office suite. Microsoft Office 2007 Service Pack 2 was released on April 28, 2009.
Excel doesn't have the AutoSave feature enabled as default, you have to add it. This is because it isn't always practical to have this functionality enabled. If you have it enabled and want to experiment with a spreadsheet, you should create a copy then open that so that the AutoSave doesn't overwrite the original.