Having reloaded PilotAware, at the moment it gets to a certain point showing all the script and then I just get the message 'Licence Fail for eth0 xx:xx:xx:xx and Licence Fail for wlan0 xx:xx:xx:xx' (where xx:xx:xx:xx is a MAC address) scrolling up the screen.
This is correct. This is what it should do. The next step is to request a licence with this MAC address (recommended to use the ethernet one now) from the automated server linked from the forum. You'll receive the licence via e-mail. You then connect your tablet to the PI Wifi, and go to 192.168.1.1. Go into Configure and you can enter the licence number and then go down to "Save" at the bottom.
As for antennae, I have a home made coaxial colinear in the attic for ADS-B reception. I get quite a lot of traffic, living about equidistant between Heathrow and Gatwick!

Something I found yesterday, I ordered a cheap external antenna to try using with the ARF, but I think it's the sort Lee already tried with no better results...but I noticed the bases were the same as the antenna given with the DVB dongle. I unscrewed mine and screwed the other antenna in, and it provided much better ADS-B reception than the stock DVB antenna. The one I bought was this one:
http://www.ebay.co.uk/itm/191458437759?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AITNot as good as the coaxial colinear though!