Not sure about our F150's, but I lifted my previous Tacoma's front with 5100's by about 2". And yes, it did affect the ride. First of all, it introduced a vibe, and beyond that, it made an alignment difficult, pretty much was on the edge. As a result, the truck did not track as nicely down the road, it was kind of all over the place if I did not watch out, if you know what I mean.
The ride was not any stiffer though.
Not sure if the F150's have the same or similar stuff going on. But it was a lesson for me, I won't do that again I think.
Looking forward to what others have to say about this, good question!
I have leveled two F150s. My '04 and now my '09 and I have not experienced any of the things that flixden mentioned above. On both trucks I drove with the stock tires for a small amount of time after doing it and I would say going to the bigger tires and from a "P" rated tire to "LT" made WAY more difference in ride then the leveling kit ever did.
I have a 2" Autospring kit on my 2010. Cost about $80 on ebay and free to install myself. When I was looking into mine, most people on this site had recommended Autosping. After a toe adjustment, the truck rode just the same, just higher. My tires made more of a ride change than the leveling kit.
The only thing different with the EPAS is you have to is unplug it before work begins. I was the first to find this out the hard way by following the directions at that time. After bringing that to Rough Country's attention they changed the directions and paid my repair bill.