The recent projects list only displays five items.
This seems unnecessarily limited. In practice I
have found myself going to this menu item and
looking for something only to find it is off the
list. Perhaps it could be expanded to 10 or so,
which would make it more useful without making the
submenu too large to quickly scan through?

In fact

http://projects.netbeans.org/buildsys/build-sys-ui-spec.html#File_Menu

says it should hold 10, not 5.

I will make the change. Simple - controlled by a
constant in the OpenProjectList constructor.