Okay, so I bought this book quite some time ago and only just recently finished giving it a thorough reading. Far and away the best parts of this book are the sections on character backgrounds, both by race and by class. Most of the people I've played with aren't into building deep character background. For the majority their character's background is of little interest. Some GMs insist that their players come up with good background material but to me that sounds too much like homework rather than a game. I see no point in forcing players to do up background info if they don't want to--there's no fun in that.
But with the character background charts at the front of Ultimate Campaign anyone can roll up some useful background in about two minutes. It's handy for GMs as well for quick NPC generation. Since this is Pathfinder, the various backgrounds also tie into associated traits (which are sort of half of a D&D 3.x feat).
My other favorite bit is how to roll up the outcomes of activities during downtime, such as earning some cash or training. They require a little math but not too much (I've seen much worse). The first set of rules I ever used, Chivalry & Sorcery, had a simple formula for earning XP during downtime but this is vastly better.
Next there are rules for building a kingdom (well, starting with a settlement and expanding out). These are based on the rules in their Kingmaker adventure path and a bit abstract. But that's probably a good thing because it keeps this from becoming an entire game within a game. Some people would be cool with more detail (Chivalry & Sorcery had extremely detailed rules and charts) but most RPG players don't come to the table to play a board game. This section also ties in with the downtime rules.
Finally there are mass combat rules. Frankly I didn't look this bit over too closely. If I ever do warfare or mass combat in one of my games I'll likely use Hordes of the Things (HOTT) with a lot of DMing poured over the top.
Verdict: buy it.