The iPad 1 I have lasts me two days between charging usually, even after all this time, with around 4 hrs video use, and 6-8hrs web browsing and non-gaming app usage, wifi and 3G always on, using iCloud and push notifications, before it needs charging, something to be said for non-retina, no cameras and a slower CPU.
My friends mini needs charging every night, usually it gets him from 100% at unplugging at 7am to around ~30% by 8pm so not to shoddy, his mini is WiFi only, no-3g and he reads books, uses it as an iPod "jumbo" and watches video on it whilst commuting.
My experience with iPhones has been unplug at 7am, and be at under 30% usually near 20% by 11am, requiring charging at work in order to unplug again at 5:30pm and again be down to 30-20% by the time i get home at 7:30pm, this is watching video, browsing the web or playing games, this has been the experience on all the iPhone i have owned except the 1st gen one, iPhones need to be half again as thick as they are now, so they can extend the battery to last a day,
My friends mini needs charging every night, usually it gets him from 100% at unplugging at 7am to around ~30% by 8pm so not to shoddy, his mini is WiFi only, no-3g and he reads books, uses it as an iPod "jumbo" and watches video on it whilst commuting.
My experience with iPhones has been unplug at 7am, and be at under 30% usually near 20% by 11am, requiring charging at work in order to unplug again at 5:30pm and again be down to 30-20% by the time i get home at 7:30pm, this is watching video, browsing the web or playing games, this has been the experience on all the iPhone i have owned except the 1st gen one, iPhones need to be half again as thick as they are now, so they can extend the battery to last a day,