My Mum used to cry (now and then) and I hated it too - but because she waould always try to cry in secret (if we saw her she would try to hide/send us away), and then would pretend everything was alright and try to patch things up with me even when I had been a total bitch.
She was doing her best, but wasn't (sting is ill isn;t) a good communicator and has a real fear of confrontation and disagreement.
What I really wanted from her when she was crying or angry, was for her to tell me what I cow I was being, that it was unacceptable, that I needed to stop. But she never did, and I hated that.
I have cried on the odd occassion in front of my DC (5 and 7) - generally out of frustration and just being worn down by a lot of bad behaviour and a generally bad day. I don't wail and say "look what you've done to Mummy!" or anything like that, but I have said things like "I'm tired and frustrated and the way you're behaving is also upsetting me - you need to stop". I don't think this is a problem - I know I wouldn;t have been upset by it if my Mum had said it.
I don't give them the cold shoulder, ignore them, hold grudges, or pretend everything is fine just for the sake of harmony. These things, in my book, are much worse.
I don't think there is any problem with the odd cry in front of DC - it really depends on the broader situation and relationship I think.
Those of you who have said they found their mothers' tears terrifying/upsetting etc mostly seem (from reading your brief posts) to have had other issues going on as well, which gave the tears a different context.