I have heard nothing but truly impressive stories firsthand about how incredibly well animals are treated; from BA, but mostly Virgin, where do they not only have temp control, regular checking, etc., they have a 'reception' area for people travelling with their pets... a completely separate area for check in and waiting until they board.
When I was planning to bring my cat over, the folks at Virgin even invited me to come down and have a tour!
And I was very worried, not only because of the long haul (LAX to Heathrow), but because he was an older cat as well. And some folks I've met here said they're older cats were absolutely fine.
I think the animals get treated wayyyyy better than the people. Which I completey support!