Questions about the taste of fruits in general

What distinguishes fruits which taste fruity from those which
do not?  For example, apples, oranges, bananas, strawberries,
and grapes usually taste fruity when ripe, while bell peppers,
tomatoes, cucumbers, okra, olives, and squash generally do not.
(When anyone other than a botanist mentions "fruit", what is
meant is almost always a member of the first group, and not
the second.)
 
Could you give me examples of:
 
  Parts of plants which taste fruity, but are not fruits.
  (The only example I can think of is rhubarb.)
 
  Fruits which taste fruity but are not cultivated for food.
  (And maybe some indication of *why* they aren't.)
 
  Fruits which do not taste fruity and are not cultivated for
  food.  (And again some indication of why they aren't.)
 
Ultimately I'd like to have several widely-familiar examples
of each.  I haven't been able to find much info about the taste
of parts of plants not normally eaten.  :-)
 
  -- Jeff, in Minneapolis
 
Subtract 1 from my e-mail address above for my real address.
.