Rav Nahman said there is a evil inclination in the service of God of going overboard. It is hard to know what are the exact parameters of this. I for one took myself to study of the Ari while at the Mir Yeshiva in NY and this certainly can be considered to be going overboard. After all right at the Introduction of the Eitz Chaim you have the warning and oath of Rav Chaim Vital that no one should look at his book who has not fulfilled a set of enumerated conditions. Take a look at them and you will see that no one who has looked at that book can possibly have fulfilled those conditions in the couple hundred years. No one is fasting from after Shabat to the next kidush.

  

[not to leave the subject in the middle let me say that the issue still is unclear to me --since after all i think that this learning helped me in many ways. Still  i feel i jumped in too soon and still needed to do a lot more of Shas] at any rate i do think that learning the ari for some time helped prepare me for the land of israel and the amazing light which shines there. so i would have to say that rav shmuel berenbaum was right when i asked him about thissort of learning. he said first finish shas. i said i already did. he said do it again. [of course when reb smuel said finish shas he did not mean the way some do it. rather he meant beiyun with tosphot, maharsha and reb chaim of brisk. ]