The calendar only seems to have a month view (which is too small; there's just a little flag to indicate the presence of an entry) and a day view (which is absurdly abbreviated—it only shows the entry titles, not any details, so if there's only a couple of appointments the screen is mostly blank). The day view also doesn't show the day of the week; this wouldn't be so much of a problem, except the whole app is very sluggish—so it's easy to over-scroll while waiting for it to respond, and then be displaying the wrong day.
Of course, I may be missing all sorts of better features, but as there's no manual (even online) how would I know?
The contacts list is a bit more responsive that the calendar, but not by much. It also loses all of the categorization that the Mac OS X AddressBook application has, which makes things a bit more awkward.
I guess with both Calendar and Contacts it's just about functional if you're desperate to get at the relevant information and away from your main machine, but that's as far as it goes.
Now that I'm in Mac mode, this Just Works.