Just back from my first cruise and yes the tipping thing is a little confusing. Read Tom and Mary Milano's reviews and they have a unique tipping plan. I used some of their ideas and they were helpful. We gave half of the tip to the room steward, waiter, and assistant waiter the second night of the cruise. I brought my own small thank-you cards and made them out. I waited till the second night to make sure that these individuals would be my staff for the entire trip. We had a unpleasant experience at our assigned table the first night and asked to be moved to a different table for dinner. The second table was much better. The next to the last day envelopes were delivered to our rooms for tipping. We used these envelopes to give the second half of the tips. Handing these envelopes personally to our room steward and waiters. You can have the tips billed to your account, but this seems quite impersonal and doesn't really give you the opportunity to express your appreciation of their services in my opinion.
Another great idea was the two dollar bills, although I didn't use them exactly the way Tom describes(no story as I gave them out.)They came in very handy for tipping for room service, cabs, baggage porters,bus drivers, etc. This way I always had some small money with me and wasn't stuck with only a $10,$20 or $50 bill at an inopportune time.I talked with my bank the week before I left and was able to get 50 - $2.00 bills. I will definitely do this again.