I was attempting to learn creating such panos for a very long time. Unfortunately the lens I have, Sigma 10-20 rectilinear is not very suitable to do this. One must take up to 16 pictures to cover the whole sphere. And what I did wrong for the very beginning - my trials were done in small interiors, so I used to caught many parallax errors.
But then I decided to go outside. I was taking pictures without any special pano head or tripod, just by hand, only using a metal key hanging on twine hanging attached to the lens to keep the front glass in more or less the same point. This idea was peeped from Florian Knorn (Thanks!). The outdoor results pleased me very much :-) Here are th first two panos that I already added to Google Maps.