I was listening to one of the most recent podcast from Erotic Awaking, where they answered a question from a listener wanted to know about giving up hobbies as part of a D/s Relationship.
I think largely what hobbies your allowed will depend on you, and the person your entering a D/s relationship. You should know before hand what hobbies you have that are most important to you, and if your going to be willing to give up said hobbies.
If you have a hobby that is important to you, not necessarily just when entering a D/s relationship but any relationship really, you should discuss this hobby, specially if its one that consumes a fair bit of money and personal time.
In my case I don't really have any hobbies that are so important to me that I couldn't really see giving them up, I might go a bit nuts with out least some computer time in my free time, but otherwise most things I could care less about. Part of why i even do some of the things I do is just to keep busy.
But if your hobby is really important to you, and you enter a relationship without first really stating that this is something you really enjoy doing, you should make it clear ahead of time and either find a way to continue doing what you enjoy but still allows you to be in the D/s relationship, or find someone more accepting of the hobby.
Thought I would be able to say more to this, but I guess thats really about all I can think of at the moment.