We bought the 10 day World Pass for our vacation last June from Paramount. Paramount was great to deal with; no problems there.
In regard to using the World Pass, we didn't run into any issues that weren't resolved. We did have one incident entering MGM....for some reason my DS-10 year olds fingers didn't scan right. I think that happened at the other parks as well, and they just waved him through, but at MGM, they checked out the situation thoroughly. The CM then asked if we were from outside the country and mentioned that that was an International Pass. I just said no, we're from Cincinnati. My younger kids had gone through the gate, and I was still on the outside with my DS-10. The CM wouldn't let him through, but I had to get to the little ones, so I went through and just sat on the opposite side of the fence from my DS-10 while my husband went with the CM to Guest Relations. Once at Guest Relations they decided the pass was fine afterall. Whole thing took about 15 minutes was a little disappointing since we'd arrived at opening hoping to get in early, but at that point, I was just relieved we got in. Never had another problem. Guess it could have been a fluke that could have happened with any kind of ticket. The International Question thing made me a little nervous, but again, ultimately, even after giving an honest answer indicating we were from Ohio, they let us in.
I had mixed feelings about whether it was the right pass for us, and I'm thinking that this year we might go back to the 7Day PHP. On one hand, we were there for 11 days, and it was relaxing to know that the tickets were paid for, and we could go to any park, any time, for as short or long of a time as we liked, without debating about whether we should 'use a day' or not. That was also good because it seemed our kids did best with a 1/2 day at a park and a 1/2 day just relaxing at the pool or in the room. A bonus was that Disney Quest was also included in the World Pass; definitely wouldn't have wanted to spend the money for my younger two to be admitted to Disney Quest, but with the World Pass we made two short trips there.
On the other hand, because we had the passes I was more driven to get into the parks every day....at least for a short time....and I think I ran the family a little ragged. (I know....this is mostly my personal problem and not a real problem.) They would have rather had some days where we didn't go anywhere. Net, this June I'm thinking about the 7Day PHP figuring that we can be a little more flexible, and if we choose to have more laid-back non-Park days, we'll come home with days left over for next year. (The World Pass' expire after 10 days.) At the same time, between the main tickets and the Pluses, we'll still be able to go somewhere every day if we choose to do that, and we will have saved a couple hundred bucks for our family of 5.
Guess it all just depends on what you want to do!