So I've had a chance to play around with Planetary Govenors a bit.

Although there are a couple of problems with the interface that have been mentioned, they basically work okay.  However, applying a governor from the colony manager isn't currently possible.  The colony manager is useful in this regard because it shows how many tiles haven't yet been built on, but I have to drill down two levels to get to the governor.  Further to this, it would be handy to have a tooltip showing the current selected governor options and the effects they may have on the planet's future production/research/morale/tax income.

Because planetary governors build whole groups of buildings, I think it might be an idea to make them a tab on the buildings list (where we currently have Newest, Old, and All).

It would be nice to be able to set up some notifications that remind you to set a particular governor.  For example, I would like to know when a planet reaches 2000M population, because that's usually when I start buillding economic structures.  When that governor has done its job and those structures are built, it would be great to have a subtle reminder to set the next governor (if applicable).  Just a change in the wording or a slightly different icon for the on-screen notification would work, I think.