Yesterday I decided to proceed to phase 2 of the project (Porting libzpool, ztest and zdb). And I'm happy to announce that libavl and libnvpair are already ported :)
Actually, it wasn't that difficult. I only had to change 7 lines of code for it to compile cleanly with gcc -Wall -Wno-unknown-pragmas (I'm using this flag because all files in the OpenSolaris source seem to have #pragma ident, which gcc doesn't recognize).
Now the real work begins. For libzpool to work, I'll have to implement a zfs_context.h which works with NPTL, and from the looks of it, it doesn't seem trivial :P
By the way, the ZFS on FUSE website was inacessible today because my Internet connection failed. Sorry about that.