I'm laughing because I came in from the front page - I saw the thread title, and it made me giggle. :) SO MANY people told me that when I was pregnant with #2 (my kids are barely 15 months apart). I had two in diapers for two years.
It was great! Why? Because when ds was 3 and dd was 2, they were both potty-trained at the same time. They learned together: ds sat on the toilet and dd sat on the plastic potty. And then, I had two kids OUT of diapers at the same time. It was awesome.
Seriously, though, the hardest part was trying to meet two small children's needs simultaneously for a few years there. My kids are 5 and 4 now and life looks really different than it did 3 years ago. My kids play together and when they aren't fighting ;) they are the best of friends. It rocks.
I would not have recommended having two so close together for a few years there, but having come out the other side now, I really like having them close together and seeing them play and laugh together. Super fun. :)