If I ordered a commission from someone, I'd personally think it'd be more fun if I didn't get to see it until it was completed. :> But I agree. I think they should ask/you should charge if they want to see it progress.
It might be more work than you need, considering you already have an LJ and such. Maybe use the Google list sort of thing to link to any progress shots you might have? don't know if you could do that, but maybe it'd be more convenient? xD