Also, switching to osmarenderer (also at the plus in the top right) instead of mapnik, you get the ski runs rendered, not only the the ski lifts.

Keep in mind that the PCN doesn't resize automatically (in JOSM), you need to right-click on the WMS layer and select 'change resolution'. In the top left corner of JOSM you see the current scale, when it shows 50m, it's the highest resolution, although there might be a small improvement if you go a bit below.
It can go up to 1km, but then it's only adapted to trace outlines of forests etc... Above that, you only get a white default image.

I usually have the bing layer on for quick orientation, and activate the PCN when I do the details.

^^^^ in the above comment, you'd have to replace & by a single ampersand.

More on the issue (in italian) here: http://wiki.openstreetmap.org/wiki/WikiProject_Italy/PCN

Instead of bing, you can use the newer (albeit slower) PCN (Portale Geografico Nazionale)
In JOSM, use this as WMS service: http://wms.pcn.minambiente.it/cgi-bin/mapserv.exe?map=/ms_ogc/service/ortofoto_colore_06.map&LAYERS=ortofoto_colore_06_32,ortofoto_colore_06_33&REQUEST=GetMap&VERSION=1.1.1&FORMAT=image%2Fjpeg&

In my home town in South Tyrol, BING data is > 15 years old, while PCN is from 2006