tangovictor,
First of all, by route planning I specifically mean the act of deciding where your lines should be drawn, heights, MSAs, etc, and just that. Perhaps personal opinion, but I don't think Skybook is the place to mull over routes because it is too slow, the chart is distorted compared to a CAA chart, lacks the necessary topographical features (some roads, some towns, etc) and what is there in terms of airsapce, etc is not clear. The Google Map/ MS Map integration is neat, but ultimately a gimmick (I think). If the route planner used a Jep or CAA chart and was speedy then it would probably be super in that respect.
However, I just plan using a chart anyway, so I just transfer the route to Skybook and it generates a very useful and configurable report with all the info I need, including NOTAMs plus easy access to Danger Area info and the AIS. From the aspect of obtaining the information for a chosen route, I find it very ergonomic and a real time saver (perhaps I'm just lazy).
Another purely personal take on it, is that I would prefer to a pay-to-use service as, however good the free services are, there is clearly no accountability for the accuracy of the information.
My caveat is that I haven't tried other tools like FlightStar or Navbox. People seem to rave about Navbox, but then it doesn't do NOTAMS. I specifically wanted something gather all the information together.
Hope that helps rather than confuse.