Write-back Using PowerPivot

In a discussion about PowerPivot yesterday, one of my friends stated that it wasn't really useful since you couldn't perform writeback using PowerPivot. To him this is a very important piece in the Excel budgeting process. Now, I agree that PowerPivot doesn't give you write-back to a database, but this got me thinking. we have linked tables, so why couldn't we create a write-back loop for a model that was built entirely in Excel? Well, we can!