If taking a med cruise would you tip in dollar or euro? the euro is significantly stronger if that makes a difference.
I'd like to know this too.

I have never been on a Disney cruise before but I know on other cruise lines they tell the passangers NOT to tip the people who bring room service that it is built into their saleries. I guess Disney do not do this?
Disney's own guidelines for tipping are here: http://disneycruise.disney.go.com/faqs/onboard-services/gratuities/
For rooms service, their guideline is at "your discretion".
Unless you order something with a dollar amount on it (bottled water, canned soda, boxed candy) there is no receipt, at least there wasn't last week on the Wonder, so no way to charge a tip to your room. I tip at least one dollar per item ordered, some tip more, some less. But I think the room service waiters get no more salary than the rest of the "tipped" CMs.
. I tipped $2 every time. Hot chocolate wasn't on the menu though -- I wrote it in and it was no problem.
I have a special envelope marked "tips" so if whoever orders room service they can pull out the envelope as well