I should have been clearer about that...
In Word 2003 and earlier, when you use the Insert > Reference > Table of
Contents dialog, it inserts a TOC field in the document. You can still
insert the same kind of field in Word 2007 by going through the Quick Parts
Fields dialog, or it may appear when you open a document that was created
with a TOC in an earlier version.
But if you create a new table of contents in Word 2007 by going to the
References ribbon, clicking the Table of Contents button, and choosing one
of the items from the gallery, the TOC field is enclosed in a "content
control" that appears as a blue box around the table of contents. The title
tab appears on the upper left corner of the blue box. The tab contains
buttons for "Remove TOC" and "Update Field". Putting the cursor somewhere
inside the TOC and pressing F9 to update it also still works.