our skirting is glued and screwed, with long fixings as we have insulated p/b - there's a little wooden plug covering the hole, sanded and varnished
I'd expect the gluing would be OK to start with but could come apart if the wood twists and shrinks - after all its only sticking to the outermost surface of the plaster
Guoprene, DAP and Pinkgrip etc are all great glues but none of them would be sufficient on their own to fix skirtings, architraves or other 2nd fix trim IMHO; a mechanical fixing (screw or nail) is always recommended as well. If nothing else the mechanical fixing provides the required clamping force to keep everything in place until the glue goes off. In addtion I'd recommend a biscuit joint at all mitred architraves- it's rarely ever done on site but it will stop the mitres opening up and is especially recommended on finished hardwoods as these can't be caulked or filled very successfuly if the joint does open up.