A simple spreadsheet created in Calc isn't displayed entirely correct in the record-view of the Form letter / mail merge dialog.
The spreadsheet has 3 columns:  Name, Address, City-State-Zip; and approximately 60 rows/records.  I created a simple form letter (also tried w/ an envelope), and tried the mail merge command.  Printing all records wound up only printing ~30 of them (about 1/2).  I then tried scrolling through the record view to select the remaining records for printing, and the record display is very buggy.  It displays some records properly, others are disrupted (like its trying to draw two items in the same field).  Selecting records causes even more problems.  Some are selected fine, others cause the selected records to be duplicated 5-6 times below it.  Printing is very buggy: some records don't print, others are out of order, and sometimes there are duplicates.

I used the same exact Writer file (with the fields) along with the Calc file in OpenOffice 1.0.1 and it performed perfectly.  I was able to print all records, scroll through the list, select and print a subset of the records.