Did a fair bit of motorway driving recently in my wifes peugeot which has cruise. It was not really possible to use it properly though. It was hard to find an appropritate speed to set it to due to so many varying traffic conditions. I kept on having to tap the brake, and then press resume to get back up to speed when the road cleared.
The only time it seemed any good was when I could go on cruise for a few minutes, I could strech my legs.
I seem to think it's only really any good on clear roads abroad.
By the way, I remember reading somewhere about a road tester who set the cruise control at 100mph in a Bentley around the Millbrook bowl, then climbed into the back. Just to see if he could.
