i have worn oscar in his ring sling (i have 3) every day since he was born, although for less time now. he is 2 and 15 kgs and i find it still very easy and so yummy. he will often want to walk so i pop it over his head to his tummy and hold on to his 'tail' and when he is tired pop him back up. i only bought a stroller a couple of months ago, i just didn't find the need for it, and have used it a few times - like when we went to the show to put all the 'stuff' in but i used the sling to carry oscar. i have a funny story about slings and prams, i pulled up and parked in the baby & prams section at the exact same time as another mum, i put the sling on put oscar in it (took about 20 seconds) and went into the shops, was in there for about 10 minutes, got back to the car and the woman was still putting her pram up and baby in it as i put oscar back in the car and drove off. needless to say she said to me 'i need one of those' and i gave her the info on them
in answer to your question, though, i don't think they are very comman but that's ok with me i'm not here to be a trendy mum just a stressfree happy one!
beckles