1) Part I took me about three weeks preparation, if only because I was being very (read: overly) thorough. My issue was making sure that I knew the technologies involved and how they differed from the current versions of
Java EE. Part II took me about four months, mostly due to work and planning a wedding, and Part III took no preparation.
2) Varies. The value of a certification is really based on what you believe it's worth and what you can convince others that it's worth. Otherwise, it's just a piece of paper.