I thought people didn't tell you what a nightmare it was because they'd all found it easy and it was just me who couldn't do it. I remember getting a card from a schoolfriend who'd had her first baby 5 months before I had ds1 and she'd written in it "isn't it wonderful?" I just looked at it in utter disbelief then ripped it up.
I did have two people who tried to forewarn me. A woman I barely knew sidled up to me at work just before I went on maternity leave, started off with small talk about when was I going etc. then - almost shamefacedly (perhaps because she didn't know me very well) said "er...I'm sure you'll be fine...but...er...if you're not, I mean...if you find it harder than you think...you're not the first you know, speak to your doctor about it if it's...well...if it's really bad."
I'm ashamed to say I brushed her off with some throwaway comment about "oh I know it'll be tough at first...lack of sleep...hahaha."
And another close friend, whose son was born 5 weeks before mine, was talking to me on the phone about how hard she was finding it and she apologised and said "oh, I'm going to scare you, talking like this." And I said "oh, you can't put me off now - I can't wait for this baby to be born." I rang her up, weeping and apologetic, a few weeks later.
So I think even if people do try to tell you, you don't really believe them...not til later, anyway.
Perhaps I'm part of the great silent conspiracy now - I don't often attempt to tell a new Mum to be how bad it was for me...I don't think they'd believe me. I never write cheesy "ain't it wonderful?" comments in cards though 