Thought i'd post this as it may be useful to some out there.
Recently came across some old drawings which had been drawn using only layers, of course we don't work like that anymore, but i needed to convert the Layers to Classes. Thinking the only way to do this was manually (create new class, select the content and change the properties in the OIP, thus moving it to the new class then deleting the old Layer), i began.
A few minutes in, whilst constantly thinking "there must be a better way" it suddenly dawned on me i can export this to .dwg and chose to convert either layers or classes to DXF/DWG layers in the process, then all i need to do is create a new document and import the .dwg (make sure 'convert classes to DXF/DWG layers' is selected under the 'graphic attributes' tab) and voila: all converted, works a treat.
Sorry if this is old news to some, but was a bit of a eureka moment here!