Saved workbooks using the Excel Connector are likely to fail since the new release.

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Why:

The labels for some default fields have changed with the release. The Excel connector uses these labels to identify columns in answer sets and to drive inserts, updates, and deletes.

If you are working interactively with the connector, you should see no problems, since the Describe command will automatically provide the new labels.

On the other hand, if you have saved Excel sheets, many will fail when you next attempt a "Query Object Data" to refresh them because their column headings no longer match those in salesforce.com.

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How to fix them:

If your saved sheet is close to a default object query, 
      you'll probably find it quickest to build a new replacement one from scratch.

If your sheet is heavily customized,
(For example, I have many which use a subset of fields but include formulas to make calcuations)
      you'll have a more difficult job.

I have found it easiest to:
     1) Do a new describe of the object on a new Excel sheet
     2) Display both the new and old sheets
     3) Drag and drop the new headings on top of the old ones.

This approach leaves the column orders the same as before, does not disturb calculations, and changes the headings to the new ones.
The bad news is that it can take 10-20 minutes for each sheet.

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Can we get some documentation?

I realize that you do not expect a tool which uses the API to use labels, and that you would prefer that the Excel connector present us with field names for column headings rather than labels.  And that, by posting that we should not use labels, you've reserved the right to change the labels at will.

Nonetheless, you also have a large number of customers using this tool, many of whom have saved sheets and will have this problem.

If we had a list of the changes, it would be possible to fix these sheets by updating only the changed headings - or even, to build a macro which would automate the changes. 

Thanks,

Scot