We didn't use tint. The windows have a certain amount of tint to them, and we didn't feel that more made sense for us. Blinds awnings and curtains regulated the solar gain during the day, and too much tint can ruin the evening views. It's also HORRIBLE to try and remove an aged or damaged tint job (I can remember removing a purple-ish tint years ago).
That said, we definitely tint the tow vehicle windows so we don't cook, and then I keep reminding my wife to not tap the window with her rings when pointing out something innocuous on the side of the road. :-) We used a lighter shade (35% transmission) on the front doors. This provides reasonable privacy yet we can still see when backing at night. The factory tint in back is in the 20% transmission range.
If you do decide to do it, just like on cars, you should always place the somewhat fragile tint material on the protected, interior side of the glass. If you do it on the outside, it'll be a mess in short order as the tint material is damaged by branches, road debris, etc. Seems like you'd be in the 35-50% range for the best results. They make some 35% mirror tints that would give you the ultimate in daytime privacy while only blocking some of the sun. Check out 3M's window film site for more.
Hope that helps.