I have 4 dogs. I've had dogs for my whole life
http://br.pg.photos.yahoo.com/ph/shatte ... r=/ab21scd
None of them ever attacked anyone for no reason. They've attacked people trying to get in the back of my house, jumping through the wall, so I guess that's ok, as they were protecting the house.
They can stink, but only if you don't take care of them. Washing FOUR dogs may be tiresome, but if you have only one, and it isn't a big one, it won't be that bad. People waste more time washing their cars
When they are young, they are full of energy, and yeah, the can destroy your stuff. My Amiga Dune 2 disk 4 was baited by one of those dogs, and it was amazing that disk was working. My mother and sister have lost MANY shoes to another dog. This can be really annoying but, after they grow up, this usually stops (Unless you have a Labrador, which is beatiful but a pain in the ass sometimes, as they seen to NEVER grow up).
And their parasites.. well, they can give you trouble sometimes, but this will only happen if you don't care about your dog. Clean it once or twice a week (If the dog stays INSIDE your house, twice is the minimal, three times a week would be better), and if fleas or anything else happen to appear on it, just give the dog the treatment it needs, and quickly. Yes, this means spending some money in medicines indeed.
And be read for shit. Yeah, real shit, dogs poop, like any animal. To clean it may be messy sometimes.
And depending of the dog you have and the area you live, they can be noisy and annoy neighbourhs. A dog barking in the middle of night can be REALLY annoying.
Those are the main cons IMO.
But honestly, those are really small things, at least for me. A dog can give you so much love that you just won't care about everything else. And yeah, they are really cute most of the time, they are fun to play, and it's just great to get back at home and see at least someone incredibly happy just because you are back.
The only REAL bad thing about owning a dog is that it will die someday, and this day usually is a very very sad day for the family. I've lost a couple of dogs in my life, and it's hard to cope with it.
Regarding you cat, I've seen dogs and cats living together many times. If they are in the same house, that's not a issue usually. My dogs do hate cats though
But I would rather think about my money and my nerves. Dogs are cute, Babies are cute, but I find them cute for five minutes and then they can go away again. I guess your kids will feel the same; they find them cute, but MAYBE will grow tired of the responsibility that comes with them. 
)
). He's probably the most loved dog in the hood too as everyone and every other dog knows him and wants to play with him (even the "not so social" dogs). He's also the only dog allowed in the Elderly home further down the street where my grandmother lives.