I have used the keurig water filter cartridges twice now and there is one thing that I have definitely noticed...the taste.  Yup, for the first 3 or 4 days there is an "acrid" taste to my coffee, since I only have a cup in the morning it's not like I'm tasting this because I drink to much, it's very obvious since my taste buds haven't been killed by coffee or smoking.  However, over all I think it's doing it's job as designed...maybe I need to soak the filters an hour or so in a separate cup of water  before making the first cup of coffee...