I had three attempts when they had to give up - couldn't get into a vein and ended up sore and like a pin cushion. That was about 7 years ago and I haven't tried since due to being pregnant (3 times) or breast feeding.
The nurse has trouble getting a blood test and it was a nightmare having a line put in for a drip - ended up black and blue!
I would love to be able to still, I had managed sucessfully about 6 times before the problems