Sonia asked a question on the last post which may have some relevance for others. As you may remember she is making some nice covered jar forms with cap lids kind of like small ginger jars. The problem she has run into is that the opening at the top doesn't line up with the base, as if it has been pushed off that central axis. This can sometimes be more consequential when you have a multiple part pot like a covered jar form where the difference is worst at the area that the lid sits. This only exagerates the inconsistency and can make it a frustrating resolution. The lid sits at an angle or noticably off center.
I will have to watch your process to help you uncover where this difficulty is being introduced, but there are some typical problems that might help explain what went wrong ( I am of course assuming that it isn't an issue related to uneven distribution of the clay through either centering or opening the form). One issue might be that the clay has twisted out of its proper round distribution. Julie, Teresa, Jayne and I were discussing this just yesterday at an impromptu group potting session. Coincidentally all three are using porcelain these days and this issue is perhaps most severe with that clay. What can happen is that as you apply pressure to the walls inorder to thin them out the water disapears from the surface and creates more and more friction the less water there is between your fingers and the clay. This drag can twist the clay so that it is distinctly off center. As the clay dries out it can even get worse as the clay shrinks and unwinds unevenly.
Another possibility is that picking the pot up off the wheel was done in such a way that a tilt was introduced into the shape. If you are careful to lift the pot straight up and set it gently straight down you should minimize the distortion. If your pot is simply too thin or shaped in an exagerated way I endorce using the pot lifters to avoid these complications. While I try to promote a fearless attitude as a means of problem solving issues through direct experience of the clay, there simply are those times when you can't do what you want just by hand and need to use tools like pot lifters and bats. If this is where the problem is being introduced you have my blessings to use either of those tools.
Good luck and happy potting!