I always compile with as many warnings enabled as possible, and I'm currently getting ~50 from Eigen which clutter the output (the number keeps growing as I use more features; reaching 50 has motivated me to ask about it!) So I'm just wondering what the stance on warnings is here.

(the ones I see are mostly about implicit conversions — almost all are "long->size_t" or "unsigned int->int" — and a couple of shadowed variables)

Is it worth reporting these, or are they considered not worth fixing?

We do try to get rid of warnings. I guess none of us regularly compiles with these flags. It's definitely worth reporting at our issue tracker at http://eigen.tuxfamily.org/bz/ , though it's not necessary to list them all (compiling our test suite with these warnings enabled will catch most if not all occurances).

OK, I've posted bug 640 http://eigen.tuxfamily.org/bz/show_bug.cgi?id=640