@ zzzzzz
+1 for the Mineral Spirits route (worked for me in the past). Also, had success with Mother's Chrome Polish (no, really). But surprisingly no one's mentioned this yet. I recently came across and now just go with "nu-glass"
http://www.autogeek.net/duragloss-nu-glass.html (available at Napa Auto Parts and other places). This should solve your problems.
BTW, wouldn't recommend using anything on your mirrors. The chemicals in these products and the elbow grease necessary to work it's magic will not only munch on your water spots but feast on the silver reflective coating on the back side as dessert, leaving you a nice clean glass with a black backing. Much better to just replace that glass entirely (nothing like a minty-fresh glass mirror to look behind you with!)
Hope this helps.