It turns out that [Today] and [Me] can’t be used in calculated fields in WSS lists.
However, there’s a bug (or feature) which allows us to use at least the [Today] any way.
In a list create a column with the name “Today”. It doesn’t matter but use the Date field type.
Now in a calculated field it’s possible to add the Today column and use it in a calculation like the age of something in years: =DATEDIF([Born];[Today],”d”)/365
Then delete the Today column – and now we’re set. WSS then replaces [Today] with the current date and the Age calculated field is filled with the Age in years.
Weird but true.
Here’s a some more reference information on calculated fields: