OK, here's my first stab at creating an Excel macro to convert AncestryDNA format to 23andMe format. That format can be used with many 3rd party utilities. It requires Excel 2007 or higher. I haven't tested it with OpenOffice etc.

https://docs.google.com/file/d/0B-wpDkkP5x0oRjQ3aS1haGM4REk/...

Please let me know if the instructions in the spreadsheet are clear enough, and if your output file works with David Pike's utility http://www.math.mun.ca/~dapike/FF23utils/diffs.php when you compare it to your 23andMe data. If you haven't downloaded your 23andMe data since it was converted to Build 37 (~ August 2012), you'll need to do a fresh download.

I don't want to clog up this thread with differences reported by Pike's utility, but I would like to collect some. Please send them to me privately DNACousins@aol.com. There do seem to be a few SNPs with different strand orientations (e.g. TT at AncestryDNA is AA at 23andMe).

If I hear back about problems, I'll remove it and try again.

Ann Turner