Can't tell you what this one does, but I was on a cruise earlier in the year (on a similar floating behemoth), and we did a stately 24 knots.
That's pretty standard for cruise ships. Ocean liners are a bit faster; the QM2 is rated at up to 30 knots, and the SS United States (1950s) was designed to go 38+, which is faster than some of our warships (at least, the unclassified speeds).