::Prokaryotes do fine without it, but they also have two outter membranes. The inner of the two takes on many of the functions of eukaryotic membrane-bound organelles such as the golgi.  Many of the eukaryotic proteins found in the golgi that embed proteins in the membrane are homologous to proteins found in the inner membranes of prokaryotes.  So in a sense prokaryotes do have a golgi, or at least something functionaly similar.  Erythrocytes, like Seraphine said, have no golgi nor most other organelles for that matter.  They are pretty much gutted before being released into the blood.  But I think even this is pretty rare for eukaryotes.  Most species' red blood cells get to keep their nuclei and various other entrails. (Mommy always said I was special.  I guess she was refering to my lack of nuclei)  But, for the most part eukaryotes need their golgis. Cells need a steady flow of proteins moving to the membrane, which, for all of us "higher" species, means we need our precious golgis. So I guess Seraphine said it best...  "yes and no."   

 == What are the major unknowns left? == 
 I just took an undergraduate module on general biology and am extremely fascinated by this Golgi apparatus. But unfortunately very little information is available in the textbook - it seems Wikipedia has more info! However, I think it would be helpful if we knew what exactly are the major areas of the Golgi apparatus that remain unknown: Are the transport systems (to and fro) fully understood? How are the vesicles formed? Are the metabolic processes all described? Is there a list of the proteins which are synthesised/modified at the Golgi? 

 And btw, what does "a multi joined membrane-bound accumulation" mean? Is that the way biologists describe such structures? 

 
 : Thanks for the words of praise, this article is somewhat of a pet of mine. That "multi joined membrane-bound accumulation" snuck in one one of my days off by the looks of it, I'm assuming the editor just meant to say, in a round-about way, that the structure of the Golgi is basically just a bunch of joined membranes. I removed that little section as it didn't really contribute anything which wasn't already said. 
 :There are still many unknown when it comes to the Golgi, you've touched on quite a few though. These are all valid questions, and a quick perusal of recent scientific literature confirms that people are indeed asking them. Use your institutional gateway to access journal articles - if you find anything interesting be sure to put it in the article! Cheers,  ''''' ♠ ''''' -