Product review (5 stars): OMFG, wow!!
I was replacing these filters approx. every 6-9 months, (we are a 3 person household), and never noticed a difference other than in pressure (indicating that the filter was getting 'clogged').... this time, I lost track of things and it's been over a year (year and a half, maybe) since we replaced the filter.  The pressure was really low, but when I installed the new filter, man what a difference!  Not just the pressure this time, I could actually TASTE a difference in the water.  I've always been a little skeptical of these sort of things, but I'm a believer now!  Just wish amazon would offer a 'subscribe and save' feature for this since it's the kind of thing that you regularly replace.