The one thing I learned the hard way (at least I don't remember it being documented) is that all formatting needs to be applied as the LAST step. Even things like row height and column width. Insert all your data, first, then apply formatting.
CAVEAT: If you are inserting a number as a string and need to keep any preceding zeroes, then you have to insert the data, apply the formatting (be sure to include "dataformat='general'" in the format), then reinsert the data into the same cells as previous. Another thing I learned the hard way.
HTH,
^_^