The Boo Reader binary definitely includes the pieces of the following:
6) boehm gc
10) IBM's ICU
11) fonts by URW
And probably more not readily-identified libs. Not all of above is (L)GPL but enough, I think, to make them obliged to make source code available.
Funny thing is that Mobipocket code is compiled in too (with gcj). I wonder if that means it'll have to be open-sourced too.