How to keep pine needles out of a gutter?
I installed the foam strips on my gutters last fall for this very reason. The design is that leaves should just blow off. 

Does it work with pine needles? Eh...sorta. The problem is that they don't blow off like leaves do...they tend to just sit on top of the sponge, but that seems OK as water still seeps into the sponge fine and drains away. I still have to brush off the needles once a year, but that's a lot easier than digging them out of the gutters by hand.

The only drawback is that in a really heavy rain, in some areas, the water is hitting the gutters with such volume that it can't all soak in and overflows. This really only happens in the valleys on my roof. That said, I have a poorly designed house with a roof line that wasn't well thought out for drainage so that's more the architect's fault than the gutter sponges, methinks. 

I live in the PNW so we're talking lotsa rain + lotsa pine needles. If I were to design a house from scratch, I probably would design it to forgo gutters completely...I'd have large overhangs, properly slopped grade, and then likely those 'rain fins' to help spread the drip line out a bit.