Its certainly helped Murray progress from one level to the next. Having said that I think there's a difference mentally between players like Murray and Gulbis - even if somone like Lendl were to go in and coach Gulbis, I'm doubtful his attitude would change. Murray's career is based on winning major titles, and he's always had the desire to do that. Gulbis has spent his entire career as an underachiever, and is quite happy to knock about making a career out of the game. He definetly has/had the talent to be a much better player, I think most of the time he just couldn't be bothered. A lot of people have suggested this is because he's been loaded his entire life, regardless I don't think he ever reached his full potential.