I played a cavalier in a friend's game. We had townsfolk interaction, one overland encounter, and a short dungeon. My bullet points:
There will be a great lean towards small PCs due to the fact that it's not an issue to bring our mounts indoors.
I increased my bear's intelligence to 3. We discussed it and figured tricks were no longer necessary since the bear could somewhat understand actual language now. A sidebar in the book regarding intelligent companions would be most helpful.
Challenge seemed as if it made a consistent impact on the encounters. I had to delay in order to use a good challenge/charge at the beginning of most encounters. The once per encounter aspect of the challenge seems to be an excellent limiting factor.
After the challenge target died, I tried to position for charges. This would draw Attacks of Opportunity which were sometimes directed at my mount which I used my ride skill to negate nearly every time. My high AC made me a great target for sinking opponent attacks of opportunity.
Sidebar on how to do Spirited charge would be nice. We houseruled that I just went THROUGH the enemy. We still aren't sure if I should be going PAST them or THROUGH them, though.
The oaths came into play, actually. I refused drink at the inn before we left for the dungeon due to my oath and then later recieved a big bonus to some poison saves against giant scorpions. This frustrated the DM because the scorpions weren't hitting me much in the first place due to high AC.
I do agree, however that the oaths are rather cumbersome. I wouldn't make them permanent, though. Just let the Cavalier get the bonus UNTIL they broke the oath and changeable only once per day or something like that.
Skills: do not change a thing. Excellent.
A small section on Companion magic items would also be nice. In a fantasy setting, I'd like to see items like the horseshoes in the Pathfinder Core Rulebook for different animals.