I dont mean to be blunt or bash PADI, that is for others to do mostly.
I completed my PADI OW last november, i found that the written wasnt that hard, it is multiple choice/guess, however i think you have to get like 80%+, although your instructor should go thru with you where you went wrong. I think i recall getting one wrong, but actually i found out that the answer was ambiguous as another answer was also correct - go figure. The questions and answers are pretty much like the reviews you do thru the course and the knowledge reviews at the end of the modules.
The open water is by the letter of the law pretty easy to pass with a small amount of practice/skill. However, to master or at least become confident and proficient at the skills required to make you a safer diver i would recommend finding a store (whatever agency) that devotes time in the pool to you, it will be invaluable during the OW dives and later diving. The skills can be done (assuming you are comfortable underwater) on first try in the pool, but further practice can help. I found (dont recommend this to everyone if you arent in control or are unsure about it) that if i practiced on the pool bottom whilst i waited for the instructor to get around the class that i could do the skill and got some practice in rather than kneeling watching the others try to do it (ask your instructor first in case they go into fits about you doing anything without them watching) - this was mostly to do the mask,snorkel, reg drills and the fin pivot, i didnt think i should push the instructor on the hovering although i did do that during open water (in control of what i was thinking and doing) whilst waiting thru others drills. Unless you know how/why/what you are doing i wouldnt recommend this to other divers (buoyancy drills) in case it caused trouble with instructors (ask first?).
Its not hard to pass the PADI OW, but try to get the most you can out of it. I found that the Dennis Graver book (YMCA manual) was a good addition to the info that was on the PADI CD-Rom, filled in some gaps left by the instruction i received and gave me the extra knowledge to really get something out of the dives (the instructors didnt give me much above the minimum!).