A lot of it comes down to what kind of oil you're using and a bit of personal preference. If you're using a full synthetic of any quality, 5000 Miles (too lazy to convert to km's right now) really should be fine for most. Many here still change at 3000 miles, which certainly doesn't hurt anything. If you're using what most people now call a mineral oil, which is just good ol fashioned engine oil, 3000 miles would be a good interval. This comes from over 4 years working at a Ford dealership quick service and seeing how the oils tend to hold up in all different conditions and engines. I'd also highly recommend the motorcraft oil filters, honestly one of the best filters out there in my opinion.
As far as time intervals, if you don't log many miles, synthetic should be good for 5-6k miles pretty easily, mineral 3k miles or so would be fairly safe.
I'd also be remiss if i didn't point out that this is based on a well maintained and fairly normally driven engine. If the car (and engine) are beat to hell, or you drive it like you stole it all the time, the oil will obviously need more frequent changing, as it has more work to do. Hopefully this will help give you some general guidelines though.
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