Came across a new ArcMap bug today. A staff member was trying to join an Excel 2007 file (.xlsx) to a point shapefile in ArcMap and it did not appear to be working. She only had Office 2003 on her machine so I tried it on my spanking new machine that has 2007 installed. Same result–the fields get appended but they are all blank.
I discovered, however, that when I had the table open, if I switched form showing ALL records to only the selected, Poof!!! The values filled in. From there I was able to successfully export the data to a new shapefile that always showed the values.
I have an inkling that the file name, which contained space and other special characters, may have been a factor.
August 11, 2010 Addendum:
I was just working with some more and, after joining a table to an Excel table, having all the fields look blank, I discovered that if I close and then re-open the table all looks good–all fields have values.
Another problem I had is that even after successfully joining a table to the Excel table and creating an XY Event Theme from it, I was unsuccessful in exporting it to either a shapefile or a personal geodatabase feature class. My personal opinion at this point would be to convert the Excel file to a different format before working with it in ArcGIS.