I actually love the mobile order for counter service. I use it all the time and prefer it to standing in line to order. It's so much easier to just hand the phone around to everyone in my party than it is to all crowd into the line (often behind groups that never seem to look at the menu until they actually get to the front of the line) and have everybody try to say their order to the cast member.
With mobile order, I'm also more likely to get exactly what I want, including special requests, because I can see precisely what I wrote down and not have to rely on the understanding between me and the cast member, which doesn't always translate.
I also think mobile order is WONDERFUL for helping to find seating in counter service dining areas. My pet peeve is when there is a single kid sitting at a giant table holding it for their family ordering food, while people who actually HAVE food are walking around desperately trying to find somewhere to sit down. The restaurants are designed for a certain throughput, and when people do that me-me-me table-saving routine, they gum up the works for everyone. With mobile order, not as many people are accessing the dining areas until they have their food, so there's a better chance of actually having somewhere to sit.
When it comes to whether I can get what I want, over Labor Day in
Disneyland there were long waits for mobile order, but I learned my lesson pretty quickly and started putting orders in well in advance, and then I just planned my touring so I'd end up in the right place when the food was ready.
So in a nutshell, I love it!