I have the book so I read it before I go to bed sometimes, but I haven't had much serious time to devote to it (sort of). I generally prefer to start a new book when I have a lot of spare time.
I've thought over the problem stating that if an abelian group has subgroups of deg. m and n then it has a subgroup of degree lcm(m,n) (up to proving that factoring into cycles is the same as a prime factorization, which I'm not sure of), I just haven't had time to write up a proof. I suppose I've cheated a bit because Halmos proves that you can decompose permutations into cycles, and that's the basic idea of the proof of that subgroup problem (the last step is non-trivial though).
From Halmos, I have a pretty good feel for the basic structure of groups (quotient spaces, direct sums, permutation groups), so I figure that chapter will go fast (at least the first half), then it depends how much ring theory I can get through; I'm pretty hazy on the specific types of rings.
Herstein purposely doesn't cover category theory because it would have completely changed the book, but I'd like to know how to formulate some of his results in the language of categories. Also, I'd like to see a treatment of tensor products different from Halmos', and I think that usually calls for category theory. Not like I need to make it more complex, but Serre doesn't use category theory in his treatment of (pre-) sheaves, but I'd like to translate some of those results into the language of category theory too.
From writing this, it seems like I should get Lang... I'll need it in a year or two anyway. Even if Bourbaki has extra material, I doubt I'll feel the need for it anytime soon.