I had a friend in antenatal group who's DS got moving very early, but they had laminate floors and he developed a sort of commando crawl/glide kind of movement before the rest of use even had sitting babies . Carpet does slow them down, but does provide them the friction to enable 'proper' crawling!
We have wooden floors and both DCs started off by pushing themselves around backwards. I think it helps them get moving earlier. When we went to stay somewhere that had carpet (DD was crawling by them) she got awful carpet-burns on her toes!
Wooden floors (Victorian - not laminate). Ds1 never crawled - just walked at 13 months. Ds2 crawled at 11 months and walked at 17 months, ds3 crawled at 10 months and walked at 14 months. So for me I'd say the floor was irrelevant.
DS got very frustrated at first because hemade all the right movements but couldn't get anywhere on our carpet. Then one day I went to a shoe shop and had to leave the buggy downstairs - I put DS down on the floor and he just shot off - the shoe shop had that very short Flotex type carpet, which had much better traction than mine at home. Once he'd cracked it, he had no more problems at home.