There's actually a picture of a Sandy Bridge CPU here
http://www.cdrinfo.com/Sections/News/De ... wsId=27319 and shock, horror it looks exactly like a LGA 1156 CPU. That's because it is an LGA 1156 CPU. As for LGA 1155? Who knows? It was being touted as a rumour long before Core i3 and Core i5 were introduced. There were variants such as LGA 1160, and some others.
How about this little gem from Fudzilla dated April 8 2010 "...."....The next generation chipset that Intel likes to call 6 series chipset, scheduled for Q1 2011 introduction, will support socket 1155. Intel also said the same for its 5 series of chipset and shortly before the launch it turned out that the real chip has 1156 pins. Intel wanted to keep it a secret and you can easily imagine that you will need a new motherboard for a Sandy Bridge 32nm new architecture, simply as the new chip will ask for a new chipset.....".
Frankly, I find this somewhat incomprehensible but there is a grain of truth in there somewhere. I think it is probably that Sandy Bridge CPUs may not work on older motherboards, but it is nothing to do with a socket change, it's about it needing a new chipset. This is nothing new with Intel. They retained socket 775 through a whole series of chipsets including at the end P45. The latest 775 CPUs would not work on the early motherboards, but virtually the whole range of 775 CPUs would work on a P45.
So it seems to me that anything put out by any web site should not be treated as fact unless it is linked to an official source. And of course although Intel, as the first link shows, have been issuing information about Sandy Bridge for some time, the rumour and speculation will continue until the hardware actually hits the retail channel.