Interesting Microsoft knowledge base article about how windows repair works (or fails to work) Symptom of failure is that Windows Update fails to update. According to the Microsoft article the "repair" function merely overwrites all the Windows files on your hard disk with ones from the CD. The files from the CD are old, and have a bug that breaks Windows update.
It also rewrites the registry from scratch, which likely means all your installed programs, Office in particular, stop working.
The knowledge base article has instructions to download updates from Microsoft by hand and get Windows Update (autopatch) to work.
From this description, looks like Windows Repair is as damaging as doing a full windows re install.