I agree with one of the first replying posters above, that few organizations actually implement those plans.

Management may desire to use the data for "other things", but any intelligent person/organization (which are admittedly rare) will see there just isn't enough detail to use that information for performance rating.

Billing external customers is pretty much the only intelligent reason to require a time sheet. Even if that "external customer" just happens to be your boss...

-Scott