I think it would depend on what kind of books you are reading and whether you are member of any groups. I mainly read old fiction (+200 years old) and non-ficition literature, and rarely got any reactions back when I used goodreads (I quit back in June this year, due to losing the ability to adding new books).

There are, however, probable more people visiting your profile - and reading your reviews - than you think; I got random reactions and friend-invites from people now and then.