I also use a spreadsheet in years that I know will be close (that has if/and formulas to deal with minimum miles, etc). This year I'm already booked over 100k, so I havent updated it in months... but I do use Great Circle Mapper http://gc.kls2.com/ for the mileage. It's handy to be able to put in: "DFW-LAX-SJC-SEA" to see mileage together, or compare mileage as I push the circuity limits of the routing rules (ie does it make sense to fly DFW-ATL or DFW-MIA-ATL for my extra time).

Problem on AA.com is that codeshare flights dont show up with the mileage, and it seems like its getting harder to connect without ending up on a codeshare flight at times.