I still love cats, but they just plain don't got jack on dogs. Dogs are far superiour if we're talking usability, interaction and (specific) training. If done right, you can make use of the dogs superiour senses (the nose is magic) and they're just unique in their ability and willingness to hunt with us. I don't know of any actual occurrence, but maybe we could try to do the same thing with large cats like tigers or lions, but I doubt that would be a very good plan.
Dogs are willing to cooperate and team up with us, and as much as I loved my own cats and still like everyone else's, they're just too selfish and plain too limited when it comes to any social skills.
A proper dog will defend you, protect you, serve you for some respect, love and food, a cat will easily snap out of it and go for a decidedly more 'fuck this!' approach. Both are opportunistic in their readiness to coexist with us, some cats can grow really fond of their handlers/owners/humans, but you can achieve some really amazing relationship with a dog and make it do the darndest things for you in its willingness to do everything for you, whereas a cat generally sees us more like self-service stations for... everything. I really like the elegance and general cuddliness of most cats, but there's just nothing they can do to achieve Rottweiler levels of love and interaction.
Captcha: my beating heart - ooh how cute.