I think the thing about going mad only applies to taking it off the shelf. Otherwise the Death Eaters wouldn't be after it.
I also believe that the prophecy applies to Harry only, now. It could have been him or Neville but Voldemort marked Harry as his equal, not Neville, and the one to defeat him will be the one marked as his equal. Also, there's the fact that it's 'Harry Potter & The...' not 'Neville Longbottom & the...' - Harry's JK's hero, she's not going to write seven books about him and have someone else save the world at the end!!! I do agree that Neville will probably play a very important part in the fight against evil. I think the fact that he was using his father's wand the whole time is significant to his being erm...not the best wizard! Having his own wand will no doubt allow him to be a much better and more powerful wizard.
Also, agree with:
neither can LIVE while the other survives. Yes bot LV and Harry are breathing and sustaining life, but how great a LIFE do either of them have?
I took the bit of the prophecy that went 'neither can live while the other survives' to mean that neither will be able to LIVE freely while the other one is alive as well. That applies to now, even. Harry isn't free to live like his schoolmates because he has this destiny to fulfil - he is the only one who can kill Voldemort and he can't be free til he does that. Voldemort obviously can't rule the world (or whatever) while Harry's still alive because Harry has the power to kill him. If V kills H, he can really live, and vice versa.