Import/Export from Excel

We are in the process of implementation, and at the same time we are "flattening" our bills of material (removing the sub assemblies - adding their components to the final bill of material) Was wondering if anyone has experienced any issues with importing/exporting using Excel. We believe this may be causing our planned variance issues - but cannot totally nail it down. Any help or suggestions would be appreciated.

Since I originally posted this question, I thought I should also post the solution we found. We were able to conquer this by the following, after utilizing the import/export function and you verify that your bill is formatted properly, make sure the 2 cost percentage fields are populated! You also need to run the integrity analysis report to reset the low level codes. After we did these two things - our problems with this issue were resolved.