Hi,
DU is a good example of good stuff going down in the community space, I actually used Level up a few years back on our fb page but honestly, it didn't get a lot of use, my customers found it just another barrier to getting an answer but that may say more about my customers than the ap! I also found it a little slow and we ultimately turned it off, more recently ive been thinking about building an app into our page but something more generic for help/support with some low level of community integration to surface metrics and maybe hot topics etc...
The whole benefit of something like level up is that your supporting users in the channel of choice and keeping them in facebook which is a good thing but i personally feel that most customers don't care, and more personally i don't actually use FB much anymore and when looking for support i find a shift towards twitter has been made and whilst customers use both, in a world of high expectations and a "i want an answer now" culture twitter seems the winner in terms of easy and sped of use.
In terms of other doing this, the likes of orange and sony had used level up on their FB pages but i just had a quick look at they no longer appear to be using it but your account manager at lithium should be able to find some examples of other clients using the app. Personally, i think something more tailored yet generic is actually more use but that's just me.
It doesn't appear to be working on their FB page right now but Plusnet have a help and support page built for facebook which clearly signposts where to get help and whilst simple I suspect very effective.
You can access the plus page directly here