Dave
Its not an issue that you don't have an earth in your lighting circuits providing you are aware of it and have installed electrical fittings/accessories/appliances accordingly.
As there is no earth then any non standard (pendant, Batten Holder) lighting points must be suitable for that type of installation. This will include switches too. If your switch requires an earth (if it has an earth terminal) then these should be repalced too. To go even further, if the back boxes for the switches are metal and the screws holding the switch on are metal too. If there was an electrical short to the back of the box then the voltage will just sit there waiting for someone to come into contact with it. Potentially fatal!
Its understood that the cost of putting an earth on circuits without an earth may be costly and impractical. It should be carried out as soon as possible. Just be aware of your installation and what you should/shouldn't do with it.
Matt
January 2009