My TBR shelf

Some women buy shoes, some buy jewelry, others spoil themselves with spa days and mani/pedis and the like.  For me it is books.  My TBR shelf now has about 75 books on it and that doesn’t include the number of e-books I have waiting on me.  I think I may have an addiction.  It could be worse I guess.  When does it become a problem?  How many books do you have on your TBR shelf?