You know, I have had my fountain for about 6 months now, and I have yet to catch my kitty drinking from it - he must be though, because there are HUGE pee clumps in his litter box, so he's getting fluid. I'm guilty of not checking on it as often as I should, since it's in a corner of the kitchen where no one will trip over it. It's made that "low on water" growling noise a few times. I've noticed when it gets real low, that there is hard water scale on the bowl part, because I don't want to give the kitty the softened water with all the salt/potassium in it. I really should get one of those water filtering pitchers and filter his water before I put it in the fountain. I guess I'll add that to my shopping list for today .
I take it apart and clean it/replace the water probably every 2 weeks or so, and even though the filter package says every 60-90 days to change it, I change it monthly. If I start using pre-filtered water though, I won't have to change the fountain filter so often.

You know, I am so bad about a) not doing chores and b) being on the computer so much, that I have a Microsoft Works Suite calendar program that pops up reminders for me on the computer - I have things in there like "wind the clocks" and "change the furnace filter", to help my aging memory . Now I can add "clean the kitty fountain"!