Ah, yes... if you meant "is the number in the manual good, or has someone out there discovered a better psi" then I dunno exactly. But it seems that with most modern cars, the recommended setting is desirable. In the old days a little "playing" around with the tire pressure could result in improvements, but for the Focus (for just plain old everyday driving, anyway) there should be no reason to vary too much from what Ford recommends.
I think it's 35 "maximum" psi. It says on the tire, and it may be different with your next set of tires so be sure to look before filling and use a tire guage (not the guage on your gas station's air pump...it's not reliable). There's some room for error too (around 3-5 psi). Any further than that and you'll notice odd tire wear. Also, the "max psi" is at cold temperature, so don't drive for a while and then expect accurate pressure readings.
Check your pressure when the tire is cold, ie: setting all night, drive it about 10 miles or so, enough to get the tires warm, then check it again, your pressure should have increased by more than 10% of what you started with (ie: 35 cold, should be no more than 38 when hot) This will ensure your tires are properly inflated under the current load. If you load up you vehicle for say a trip or a bunch of buddies for a long trip then you need to increase your pressures. The max press on the side wall of the tire is the max for that tire not the recommend for the particular vehicle, ie: weight etc.
i don't think 17's are availible from ford on the focus.. so they are aftermarket tires, and the info in the owners manual won't be accurate for your tires. In my history of driving, tires at the recommended pressures have caused the tires to wear on the center of the tread faster than the rest of the tire, so the pressure was a little high. Higher pressure will give you better fuel milage, but if it wears the tire improperly, and you have to get new tires sooner, then it wasn't worth the savings in fuel. Most radials run from 32-35 psi cold.. start there and monitor your tires for wear, and adjust acordingly