I went back to work when DS1 was about 4 months old - and that was 2 months after having an accident where I cracked my pelvis!
DH didn't earn more than me (about the same at the time but I can now earn more)so it didn't make much difference financially but to be honest, I wanted to go back to work. I find I become very depressed when I am at home full time and DH doesn't so it made more sense for him to SAH.
When DS2 was born a year later, I went back to work full time and studied at college part time while DH was a full time SAHD to 2 sons under 2!
We both found it hard but I honestly think it worked for us - I don't think I am very good as a SAHM.
-DH will be a SAHD and I'll go back after 3-4 months. And even though we are not even parents yet (7 months pg), we are already considered bad parents - I'm the "Why have kids anyway if you don't want to raise them" and he is "Stop leeching off your poor wife, get a proper job to support your family!".
With attitudes like this, no wonder most people take the easier option and conform to the expectations-
This was and is very true for us also. Lost count of the number of times we had to defend our decision for DH to SAH instead of me, even to 'professionals' like the HV (I did actually start a thread about that!) who asked if he 'felt like less of a man because he didn't work'.
Quite often people were rude, sexist and downright insulting about it to both of us!
There's been a lot of talk recently about whether or not SAHM are undervalued - I think they are to an extent but not as much as SAHD.
Also, what has been said upthread about Dads being 'left out' was very true for DH, he stopped going to our local toddler group because no one would talk to him, even when DS started going to nursery mums seemed to avoid him :(
One of DH's best friends is also a SAHD but he is a single parents so receives none of the same critisisms.