I thought I'd just add one permutation to this thread:
I am an EU citizen, my wife is not. She has a UK visa as a EU/EEA family member. We usually go though the "All Passports" queue at LHR, but in early April the (extremey friendly) immigration officer told us that with that visa we were pefectly entitled to use the UK/ EU passport queues. As these are often much shorter we did just that when we entered last week and it was no problem at all. They did not ask for a landing card and did not even stamp my wife's non-EU passport (although the previous immigration officer had done so).