I work on the BW side of things, and it's nice to see a software bolt-on to SAP ERP that also provides "content" extractors for BW. And speaking of the "use what you need", there are a lot of extractors that you can use, but we only use three of them for what we do.
From the BW perspective, getting them to acknowledge and then fix an issue takes a bit of effort. Sometimes you almost have to actually tell them how to fix it, and then they'll fix it.
The naming standards of the cubes are a little hard to get used to at first, and how the whole Chargeback to a Billback process works. But once you've gotten through that, it's pretty easy to understand.