The 1831 census returns I have seen were mainly statistical, but I haven't seen the Isle of Man one. You used to be able to access the data online, from a study done by a couple of universities.

Try http://72.14.253.104/search?q=cache:F56Qkb8H004J:ahds.ac.uk/catalogue/collection.htm%3Furi%3Dhist-4961-1+1831+census+isle+of+man&hl=en&ct=clnk&cd=1&gl=au

This says:
The Victorian Census Project has now digitised the entire 1831 census for the whole of Great Britain and its offshore islands of Jersey, Guernsey and the Isle of Man. A copy of the full census in machine-readable form will be available from the Data Archive, at the University of Essex, in early 2005. By clicking on the appropriate links below a new version of the 1831 census, reworked according to registration district in England and Wales, and hundred in Scotland, can be downloaded.

Background to the 1831 Census

The 1831 Census was the fourth national census to be undertaken in Great Britain. Like the three earlier ones it was undertaken by the overseers of the poor in England and Wales, and schoolmasters in Scotland. Although the amount of information collected in this census was far less than was to be collected in later ones, that of 1831 was the first in which detailed occupational statistics were collected on the employment of males aged 20 and over. The census was also the first in which detailed instructions were given to the enumerators on how they were to count the population.

Sue