Comment 5 for bug 900790

IMHO every country has it's own rules for
* "Books"
* "Tax"
and there will be a lot of special issues which will have to be addressed in localisation
Example in Austria
Tax and Books are usually the same, but
* the duration can be different
* the "tax purchase value" may be different from "Books"

but "put into service" date seems to be a logical and common field, which can be used to override the purchase/invoice date.