Never paint new doors or skirtings... those that do use finish coats of gloss... and thats bad news when it comes to repainting.. all that sanding, keying, two new coats etc. No. Doors and skirtings best done just with some stain - quick to do, if gets really mucky then scrub with sugarsoap and another quick coat.
All part of my lazy approach to house painting.. stained doors contrast nicely with only use white emulsion for walls and ceilings (cheapest option and no cutting in)