I have never heard of file corruption caused by typing dates. I have heard and seen hundreds of times problems and massive wasted time because dates were typed rather than using links, but not file corruption.
However corruption may occur if date cells are linked to cells in another project or application and you have a poor network, move either of the files, rename them or over-write them. Then the file corruption dice are rolled.
Note: With Project 2007 it is essential that you install Service Pack 2 and if you use master projects install the latest cumulative updates from Technet as well.
