Do you remember the '00 and '04 elections? 3.6% would have swung the election to the D's both times. Personally, I don't relish "President McCain" but I'd rather have a president with an ACU 82 lifetime rating than one with a 9 (Clinton) or 8 (Barak).
ACU ratings don't count for much if you have a habit of voting on key issues as a liberal and consort with them to erode Constitutional rights behind closed doors. You want to vote based on an ACU rating? Knock yourself out. If McCain is elected (highly doubtful), don't start whining that he acts like a liberal in office.