Use the source Luke!
In the former times, SAP's application logic was written in ABAP - open source - in the sense that anybody could understand it. Now I obverse, despite the benefits of open source - SAP is tending to hide the source in Java classes. The newer product offerings are more closed than the "closed" ABAP applications ever were.
This is a very good point. SAP was open source (meaning open knowledge) even before open source become popular. I'm not sure if they realize how important this was for their success. From my experience, good SAP implementations depend a lot on the ingenuity of consultants that hack the user-exits and BADIs. No matter how clever the consultants are, if they cannot read the source code they cannot invent those hacks (I wonder if APO would not be much more successful if it did not hide so much in the COM routines and optimizers binaries).
Source code, plus the integrated debugger and /h is the gem of SAP. Going away from it is a BAD decision.