Well, as a customer of Three - I can't often complain. Good signal and good speed at home, at work, at the climbing wall, at the gym, at the supermerket, at the parents and up-n-down the M1 when working (well, I never seem to get call dropouts)
..but then I go to the Inlaws - only a couple of miles from Lincoln - and I get absolutely nothing! I have to go outside to make a call or send a text. Interestingly, the rest of the family (a mix of GiffGaff, Vodafone, O2) all get great signal and speed there too.
Everyone complains when the net/call signal drops - it's only human - you're paying for a service and are being inconvenienced by it's unavailability - but by virtue of it being a complaint-worthy event - we can't be doing too bad at all.