I haven't read all the replies, so sorry if its been said (too many)
As a SAHM, I think the later years are very different to the early years with a baby. Some stuff is the same, some is different. Early years (baby to preschool say) is hard slog in many senses, WTF do I do with them all day etc etc, Weetabix on the wall that dries like concrete, why do my hands still stink even though I washed them 3 times after changing the nappy, etc etc.
However, generally, you don't have to be in a certain place at a certain time (unless you have older kids) which gives a certain sense of freedom and windows for chill out zones (naps and shit)
Older kids - different. School run, which WOH parents mainly have to do as well, but then there is this blissful 5 and a bit hour window of "me time", which can also be boring depending on what you do with it. Then the after school thing, if you are there, can be weird and shit when the weather is bad and they cant play out, homework, endless fucking demands for snacks and crap TV instead of doing homework and eating the effing dinner you cooked, etc etc. Slight sense of drudge with the pay-off of that nice window of serenity while they are at school.
Then the chauffer years begin.
You can be a target for favours of working mothers (I don't begrudge this, I help out wherever I can, girls compete with each other, women empower each other as the saying goes)
Like life, things change as the years go on. The days go slow but the years go fast.
An early poster above said she hates WOHM's saying they do everything a SAHM does as well as work - I wouldn't necessarily agree with that. If the child isn't in the house, the amount of mess is not the same. If I went to work full time mine would be with a childminder after school, I'd only have to do bath and bed not the sometimes tedious bit in between. Friends who went back to work and had babies in full time nursery were happy to admit they had a nice balance of being able to drink a cup of coffee while it was still hot and coming home to a relatively tidy house because the child was at nursery all day.
On the single mother front, my husband works away a bit and I can't say that makes me "know what its like" because I have financial support, emotional support, regular sex, etc etc.
Just some thoughts really.