This. My youngest are almost exactly five months apart (one turns over on the 4th, the other the 7th), and are currently 5 and 10 months old. This is a good age gap for me, and I'd be fine with having three young dogs at a minimum of 5 months apart. I wouldn't touch litter mates with a 10ft pole.@purplesully - My family also raised two Collie mix brothers, a long time ago. It wasn't intentional - they got one from a neighbor and was just "holding" the other boy for another neighbor to come home from vacation, at which point they were just too attached. I doubt it was anything to do with being 'pack leader' as they didn't subscribe to that methodology, I think they were just easy dogs.
Another thing to keep in mind with having three puppies at once is the sheer responsibility of having three puppies at once. Training, housebraking, etc. is hard enough with one dog - multiplying it by three is just a nightmare!
Also - and this is something that not everyone considers a big deal - having multiple dogs the same age is hard. Maybe not at the beginning, but when they all start to age...it gets tragic. Even if you have funds enough at that time to cover vet expenses, the pain of losing dogs so close together is terrible to bear. I speak from experience - I lost two elderly dogs this year, and have another one who is aging (so far, so good) but losing her is going to be unimaginable.