Sorry to sound negative but how long is a piece of string?
Don't you Guys realise that the "Posts" table (actually tblThreads) uses a field of the Memo type (for the Post Body) which our colleagues at MS define as follows:
Up to 65,535 characters. (If the Memo field is manipulated through DAO and only text and numbers [not binary data] will be stored in it, then the size of the Memo field is limited by the size of the database.)
It should therefore be apparent that the Database size will be substantially influenced by the length of each post and the degree of formatting used. Basically, what I am saying is that DB size is dependent on the data stored within it. Borg's DB design is very well executed (ie normalised) and is therefore very efficient on size assuming you regularly run a compact.