How much leaked oil is too much?

[silver-S]

I've had my 2002 S for about 6 weeks now, and in that time the Boxster has started marking its territory. It's just a drop every day or so, but it's adding up, so I have begun wondering: just how much of an oil leak is usual for a 12-year-old Box, and when should I start worrying about it?

I bought the car expecting to have to spend some money on it the first year or so. Maybe this is the start.