DD (now 16 months old) was breech at 37 weeks. Went in to discuss options with the consultant four days later and she was cephalic again. She then turned at least twice (that I know) of between then and 42 weeks.
Found out she was breech - again - when I went in for a check-up the day before induction and the consultant performed an ecv there and then.
Had a quick scan (mobile scanner) to determine the position of her head etc and also the location of the placenta and umbilical cord. She was monitored for half an hour. Then I had an injection to relax my stomach muscles (as someone else said, makes you feel a bit spacey and heart races a bit, but its not horrible). The consultant left me with a midwife for about 10 minutes, iirc, while it took effect then came back in, another quick scan (literally 2 minutes) then grabbed dd by the bottom and head and turned her round in one deft action. Took all of about half a minute and was uncomfortable but definitely not painful. I was then put on the monitor again for an hour to ensure they had a good trace on dd and allowed home to prepare for induction the following morning.
I was told that if it wasn't successful in two tries, took longer than two minutes or was painful they would stop and wouldn't try again.
I sat bolt upright all night that night. After all her acrobatic shenanigans I wasn't going to give her the chance of turning again and landing me with a c-section at the last minute.
She was born in her waters (torpedo stylee ) the following afternoon 1 hr 30 mins after my first contraction.
To be honest, I refused ecv at 37 weeks as I thought the potential for her turning again was too high for it to be worth the risks involved. As it happens I was right to refuse, as she was most definitely not intending to stay put from then until delivery.
For what its worth, I also had a neat little bump and the consultant and midwives said they were flummoxed as to how she was managing to keep turning around so, contrary to what you might be told, size is no indicator as to the likelihood of your baby turning back round again even if the ecv is successful.
For me personally, I didn't want the ecv at 37 weeks, because I felt not only was there a big chance she would simply turn back again, but also I didn't want to go into labour early. Obviously neither of those were an issue at 42 weeks though.