Ali and Funkychips, both of you live well within the city?
It may be caused by the heat island (not sure if this is the right term) which is generated by a big city. Here in Manila, if I go to the outskirts of the city the weather is way way cooler, in fact when I visited my Motherinlaw at a nearby province it was really cold that I wished I brought a jacket. Hot and dry our city air is, not to mention pollution. But what can we do? For me I try to give them as much humidity as I can. There are a few ponds and tubs in the area, plus some water dishes. For me at least it has rained for the past few days (drizzle) so at least that is refereshing for the plants.
Ventricosas are the worse off, I have an amp that doesn't have pitcher, one of my amp basals died, etc. etc. The best pitchering plant I have is my beloved Gracilis
Then again they are known to give pitcher at every leaf, small and cute. My truncata still does pitcher, but slow, so does the Miranda.
Maybe, just maybe, the trick is to have some plants that have long lasting pitchers and some that are known to pitcher no matter what, so that when the other species don't pitcher, you still have some nice pitchers in other plants!
Good luck to us
TTFN
Arvin