At my $dayjob Wicket 1.4 still rules supreme, but work is under way to migrate our apps to 1.5. Our migration experiences should make a nice blog entry, but meanwhile Alexandros Karypidis has published his experiences migrating from 1.4 to 1.5:
1) Maven dependency has changed
3) Header contribution is now implemented in Component and Behavior
5) Page mounting
6) Mounting of global resources
Not too bad for a big upgrade. Of course, you can always refer to our 1.5 migration guide.