Oh where to begin? In no particular order:
Foreign call centres, where the ops read from a script and don't quite understand what you are saying. Three, I'm looking your way.
Tricksey packages that make your head spin trying to remember all the catches. Top up by so much, get such and such free. Great when it works. Orange, you stink.
Unlimited data downloads, that are capped to fair usage. No that isn't unlimited at all.
Now the positive.
I'm very happy with giffgaff so far. I like the plain simple approach to tariffs. I think texts could be cheaper though, knowing the real cost to the telcos.
More flexible topup options would be nice. If I'm down the supermarket, adding a topup at the till is handy.
I really like the free data. I am a light data user 1-2mb a day, so free is perfect. (I have to admit to being slightly annoyed by users who expect to tether their iBerries for nothing though.)
Keep up the good work. Power To The People!