Poutymouse - This is my opinion: In the hospital, Hurley made up Dave to express his negative feelings and to avoid facing the work he had to do to get better. I think the Dr. was using therapy to get Hurley to decide it was time to fight and get better, and that when he did, Hurley would make Dave go away. On the island, Hurley brought Dave back when he could no longer deal with feeling helpless and hopeless - he couldn't admit to himself that he was feeling suicidal, and used Dave to offer a form of "rescue".
Bailygp - My all time favorite TV proposal!
Nilesgirl - Good observations on guilt. I still think the primary reason that Kate killed Wayne was that she found out her mom was sick and needed the insurance $$ for upcoming treatment. His being an S.O.B. helped with that decision but she could certainly feel guilty about doing it.
O.K., I'll be the politically incorrect one - Sawyer commenting on his "convenience store" saying "Does Sayid need a job?" - favorite line!