hi -
i actually have one of these machines - and they are quite good actually (used it for about 4 week, and it were great (i then moved house, and just getting round to unpacking).
i think its great - does brews lovely (i am a coffee drinker though) but me mrs has tea, and we never had an issue with it, and never used the normal kettle - which was right next to it. just stopped using it for about two week, as we just moved house.
HOWEVER.... (it had to come didn't it?),
me mrs son and his father in law, both had one and they said they got just under two months use with it, and then the temperature just starts to decline (until, at around two months old), the water from hot dispenser on it, is just about tap water warm.
but ours has not come to that stage yet (fingers crossed)... but there is just one thing with it - it is noisy for what it is, and the water from hot does not come out in one smooth flow (as on the tv ad) but more of a one pump per second pump action, for about 15 seconds to fill your cup - so its not 3 seconds as claimed. and its not a smooth smooth flow.
but to answer your question - the carteridges are easy to get hold of - about �5 from amazon.co.uk.
for �60.00 (what i paid for it) - i would look at a nice good quality rapid boil conventional kettle.