Waste of time, increase size of gerber file ands generaly make life difficult, I'd stick with standard retangular pads, IPC-7351 spec and the various wizzards gives you the choice. would be hardpressed to recall a customer or company that actually uses rounded rectangles. There were problems with lead freein the early days and some AOI machines would fail assemblies because of the flow problems. but in the last few years I haven't seen the problem as much (lead free is now a mature process, having been around for 10+ years with some companies and at least 8 with others) and processe, fluxes, solder pastes have moved on.
The problem with Gerber (and ODB++) with rounded rectangles is these often have to be drawn instead of flahed (depending on CAD system used), greatly increasing the size of the files. For paste screens there are some advantages, but generally the process of creating the screen means that the corners are never super sharp, but tend to have a small radius on them.
Some bottom terminated components have bullet shaped pads to match the shape of the pad, but for others I dont bother,its extra work and hassle over a problemthat is not as big as it was origionaly thought to be.
Just my view, having tried both types in the past and workinng with numerous customers, I have found no real advantage.
Marc