For web-sized pics (I use 750×500 px) I tend to use a very small radius (0.2) and 200-250%, then apply it once and if nothing starts aliasing yet a second time, then fade back to where the aliasing started. Often some areas start aliasing sooner than others and you need to restore these with your original resize. One of many ways of doing this is duplicating your image before sharpening, then erasing the bits that went wrong (so the original non-sharpened resize shows through).