I've got the MouseWaits app on my phone. It gives you the current wait times for rides, attractions, and several food & beverage establishments where lines tend to build. I look at it every once in a while when I've got nothing better to do. The current wait for a Starbucks beverage in Disney California Adventure is 14 minutes. Not bad for a Sunday. It's been worse, much worse, as now Disney people can get their park fix and Starbucks coffee fix in the same location.
There used to be a Starbucks about a block from my house in a supermarket. Sometimes I would stop by there for a mocha or latte on my way to work. I would cringe when I would see 3 people standing in line in front of me. That Starbucks closed down but I would say it was more the fault of the struggling supermarket than Starbucks. So now the closest Starbucks is a standard strip mall establishment about 2 blocks from my house. If I stop by there in the morning, there are usually 5 or 6 people standing in line. Since I'm usually in a hurry, I pretty much skip Starbucks in the morning now. 5 or 10 minutes is far too long to wait.
So now I have seen pictures from the DCA Starbucks found inside the Fidler, Fifer, & Practical Cafe (still a dumb name) on Buena Vista Street. From some of the pictures I have seen, there must of have been at least 30 people standing in that line. But that's different. It's one thing to be standing in line for a Starbucks before going to work were time is everything and quite another to be standing in any line in a Disney park where line standing approaches something of an art form as to keep yourself amused and entertained while doing nothing.
As for the Starbucks itself, from what I have read, they can whip out the basic menu pretty well but if you are one of those "snobs" who rattle off a single beverage that takes two minutes to explain, well then, chances are you may be headed for disappointment. This is a Disney park, keep your special orders for the real professionals and stick to the basics.