I actually did a course on family history and one of the things we were told was that the census was often filled in by the person who was in the house at the time, who might have been someone like a lodger who didn't know all the correct details (or spellings). My maiden name is continuously mispelled (one of the reasons I changed it), but fortunately my ancestors were so unadventurous that they never moved anywhere so I always knew it was them however cunningly disguised!

Have you been watching Who Do You Think You Are? It's been like a whole window opening on the past.